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------------------------------

Subject: 8b.3   Snakebite flats
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 23 May 2001 14:13:14 PDT

Snakebites, otherwise known as pinch flats, are so called because they
usually cause adjacent punctures about 10mm apart (for tires with
about a 25mm diameter cross section).  They occur when the tire casing
bottoms on the rim, causing a compression failure in the tube for both
clinchers and tubulars, much like pinching the cheek with thumb and
forefinger.  The finger tips simulate the tire casing and the cheek
the tube.

Reasonably inflated tires can bottom when crossing RR tracks, riding
up a driveway with a raised lip at street level, or riding on rough
roads with ruts and rocks.  Although higher inflation pressure helps,
it does not guarantee protection.  Watching how, and how fast, such
obstacles are encountered helps more.

Because latex rubber of tubes commonly used in better tubular tires is
several times more stretchable than common butyl rubber, such tubulars
are less susceptible to snakebites.  When sheet rubber is compressed,
it stretches laterally like a drum skin, and the farther it can
stretch the less likely it is to tear.  In contrast, when ridden over
such obstacles, tubular rims are often dented without the tire going
flat.  However, because thin latex tubes hold air so poorly that they
must be inflated daily, snakebites from under-inflation were more
common in the days when most riders rode tubulars.

Snakebites can be identified by inspecting the tube under grazing
light that will reveal diagonal tire cord impressions at the
perforation.  This is especially important when only one hole occurs,
the other not penetrating.  Riders have claimed that the hole occurred
spontaneously on the underside of the tube and demand reimbursement.

Underside snakebites, the least common, occur mostly on fat MTB tires
that are often ridden with low pressure on soft terrain.  At low
pressure, such a tire can roll to one side and pop back, without
disengaging the rim.  A snakebite caused by this mechanism appears on
the underside of the tube similar to laying your head to one side
while pinching the skin at the Adam's apple.  Such flats are
erroneously attributed to rim tape failure and other obscure causes,
when in fact it was under-inflation that can no longer be assessed.
Here cord impressions also give evidence of a snakebite.

------------------------------

Subject: 8b.4   Blowouts and Sudden Flats
From:  Jobst Brandt <[e-mail]>
Date:    Fri, 11 Jun 1999 7:42:45 PDT

Bicyclists often report tube failures that they believe occurred
inside the tire casing.  They believe these are caused by a faulty
tube that split or that the rim tape failed.  However, they also heard
a bang after which the tire was flat.  On removing the tire casing
from the rim with tire irons, they discover a burst tube with a large
slash.

If there was an audible bang, then the tire was off the rim.  That the
undamaged tire is still on the rim afterwards proves only that tires
usually fall back into place after exposing the tube.  A tube cannot
blow out inside the tire with a bang, because a bang is caused by a
sudden change in volume, an expansion.  Such an expansion is not
possible within a tire casing.  Beyond that, the resulting clean slash
in the tube cannot occur from rim tape that would cause a gradual
failure along an abraded line that extends beyond the end of the
split.  A burst into a rime hole would cause a starburst hole that is
smaller than the rim socket because the tube shrinks when no longer
inflated.

Tire blow-off occurs most commonly on tandems where substantial energy
of descending mountain roads is converted to heat in rims by braking,
in contrast to a single bicycle, where most of the energy is
dissipated by wind drag.  Rim heating has two effects, of which
increased pressure is probably the lesser one.  Heat softens the bead
of the tire so that it can squirm out of its clinching seat in the
rim.  Tire casing flex at the load point works the tire so that it
squirms out of engagement.  Heat also increases lubricity of the bead
against the rim to facilitate creep.  Formerly, base tapes made of a
dense gauze-like tube, filled with Kapok, were offered for mountain
tourists.  This padding served as insulation to prevent the rim from
heating the tube  and increasing pressure.

Short tubes, that must be stretched to fit on the rim, can cause tire
blow-off.  A stretched tube will occupy the space on the bed of the
rim where the tire bead should be to make proper engagement with the
hook of the rim sidewall.  The tube under the bead of the tire can
prevent proper engagement with a hooked rim to cause a blow-off even
without great heat or pressure.

Valve stem separation is a failure that is less dangerous because it
usually occurs during inflation.  It causes a slow leak when occurring
while riding, as the vulcanized brass stem gradually separates from
the tube.  When this occurs, the stem can be pulled out entirely to
leave a small hole into which a valve stem from a latex tube of a
tubular tire will fit.  Stems from tubulars have a mushroom end, a
clamp washer, and a locknut, that fit ideally.  Such a used stem
should be part of a tire patch kit.

------------------------------

Subject: 8b.5   Blown Tubes
From: Tom Reingold <[e-mail]>

Charles E Newman writes:

$      Something really weird happened at 12:11 AM. My bike blew a
$ tire while just sitting parked in my room. I was awakened by a noise
$ that scared the livin ^&$% out of me. I ran in and found that all the
$ air was rushing out of my tire. How could something like happen in the
$ middle of the night when the bike isn't even being ridden? I  have
$ heard of it happening when the bike is being ridden but not when it is
$ parked.

This happened because a bit of your inner tube was pinched between your
tire bead and your rim.  Sometimes it takes a while for the inner tube
to creap out from under the tire.  Once it does that, it has nothing to
keep the air pressure in, so it blows out.  Yes, it's scary.  I've had
it happen in the room where I was sleeping.

To prevent this, inflate the tire to about 20 psi and move the tire
left and right, making sure no part of the inner tube is pinched.

------------------------------

Subject: 8b.6   Tube Failure in Clinchers
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 13 Oct 1997 15:02:23 PDT

Riders occasionally tell about a tube that blew out with a loud bang
INSIDE their tire, leaving the tube with a long slash.  The tube blew
out, but not as described.  If there was a bang, the tube was outside
the tire.  That is, the tire lifted off the rim and fell back in place
after the tube burst.

Tubes do not burst inside tire casings, although they may leak, the
most they can do is give off an audible hiss, assuming it is otherwise
quiet enough.  An un-socketed double walled rim can make a dull pop if
the tube is exposed to the inner rim volume.  The concept that a tube
can explode inside a tire is dangerous, because it leads people to
believe that tubes can mysteriously fail without apparent cause INSIDE
a tire.  With few exceptions, the cause is an improperly mounted tire.

Without understanding the cause, a rider may continue to risk a
blowout, without realizing that tire lift-off can be caused by the
tube lying between the rim and the tire bead.  In this position, the
tube prevents the tire from seating properly in the hook of the rim, a
condition that, under the right circumstances, will cause a blowout.
This cannot occur inside the tire casing.  To prevent blow-off, the
tire seat must be inspected by pushing the tire away from the rim,
upon which the tube should not exposed at any point around the tire.

Valve stem separation is another common failure, but it is less
dangerous because it usually occurs while inflating the tire.  If it
occurs while riding it causes a slow leak, as the vulcanized brass
stem separates from the tube.  When this occurs, the stem can be
pulled out entirely to leave a small hole into which a valve stem from
a latex tube of a tubular tire will fit.  Stems from tubulars have a
mushroom end, a clamp washer, and a locknut, that fit ideally.  Such a
used stem should be part of a tire patch kit.

------------------------------

Subject: 8b.7   More Flats on Rear Tires
From:  Jobst Brandt <[e-mail]>
Date:    Thu, 22 Jan 1998 18:15:42 PST

Many sharp objects, especially those that lie flat on the road like
nails and pieces of metal, more often enter rear tires than the front
tires.  That is because the front tire upends them just in time for
the rear tire to be impaled on them.

For example, nails seldom enter front tires.  When dropped from a
moving vehicle, nails slide down the road, and align themselves
pointing toward traffic, because they prefer to slide head first as
they would when laid on a slope.  The front tire rolling over such a
lengthwise nail, can tilt it up just in time for the rear tire to
encounter it on end.  I once got a flat from a one inch diameter steel
washer that the front tire had flipped up so that the rear tire struck
it on edge.  When following another wheel closely, the front tire can
get the "rear tire" treatment from the preceding wheel.

The front wheel set-up effect is especially true for "Michelin" wires,
the fine strands of stainless wire that make up steel belts of auto
tires.  These wires, left on the road when such tires exposes their
belt, cause hard to find slow leaks almost exclusively in rear tires.

When wet, glass can stick to the tire even in the flat orientation and
thereby get a second chance when it comes around again.  To make
things worse, glass cuts far more easily when wet as those who have
cut rubber tubing in chemistry class may remember.  A wet razor blade
cuts latex rubber tubing in a single slice while a dry blade only
makes a nick.

As for pinch flats, aka snake bites, they occur on the rear wheel more
readily because it carries more load and is uncushioned when the rider
is seated.  The rider's arms, even when leaning heavily on the front
wheel, cushion impact when striking a blunt obstacle.

------------------------------

Subject: 8b.8   Tube and Tire Casing Repair
From: John Forester <[e-mail]>

  There sure seems a dearth of knowledge about patching both tubes and
casings.

  Yes, the idea that tubes could be patched without liquid cement was a
good idea, but only as an idea to research to see whether an adequate
adhesive could be developed. So far as I know, all the peel and stick
adhesives are very viscous liquids. That means that they don't harden and
therefore that the air pressure will slowly leak into and through them. If
the viscosity is high enough it will take the air under pressure a long
time to form another leak. A glueless patch of the peel and stick variety
cannot have effective solvents in it, because the solvent would evaporate
during storage. Even if the patch were sealed inside a container that
prevented the evaporation of the solvent, the system would have the problem
of getting enough glue onto the tube and then letting the solvent partially
evaporate from the open joint for the joint to be made. You might as well
use the old system.

The problem that some experience is that they find the cement hardened in
the zinc dispensing tube. The answer to that is to buy the cement and its
solvent in bulk and carry a small quantity in a small jar with a screw cap.
A metal jar would be most useful, but I do not know of any common source for
such. Small glass jars are commonly available and last well enough.
Periodically, examine the cement inside and top up with solvent if it gets
too thick. Because the cement tends to glue the cap to the jar, it is
desirable to wrap both the jar and the cap with several layers of adhesive
tape to provide a better gripping surface at a larger radius.

Two kinds of cement are available. The traditional cement is rubber cement,
Camel #12-086 Universal Cement, available at tire shops. The other cement is
contact cement, available from hardware stores.  While the modern
formulations often are non-flammable and use chlorinated hydrocarbons as
solvents, buy the flammable kind, if available, because the chlorinated
hydrocarbons are detrimental to rubber. (Very important for diluting rim
cement for tubular tires. Not so important for just tire patches or boots
because the solvent evaporates.) In any case, use toluol as the replacement
solvent, available at hardware stores.

The tube must be cleaned before applying the cement. Stick medium sandpaper
to tongue depressors and cut to lengths that fit your patch kit.

  Cut casings are repaired with an internal boot. Satisfactory boots are
made from cotton trouser fabric or from lightweight dacron sail fabric.
These must be cemented by contact cement, not tube cement. Cut pieces of
suitable size, so that they run almost from bead to bead when laid inside
the casing. Coat one side with several layers of contact cement and let it
dry completely before storage. Before applying, coat the inside of
the casing with contact cement and press the boot into place before the
cement dries. Wait about ten minutes before inflating the tire. If you wait
too long, the cement really hardens and there will be a narrow spot in the
casing because of the greater strength where the patch reinforces the
casing.

  It is probably possible to use contact cement as the tube patch cement.
Do not use tube cement for boots; it slowly creeps and allows the boot to
bulge. So carry a small jar of each cement, or one of contact cement.

  Contact cement is suitable for closing the outside of the cut also, but
it must be applied in several layers and allowed to dry thoroughly before
use, or it will pick up particles from the road. Duro Plastic Rubber is a
thicker black rubber paste that can be applied in one layer and left to
harden.

------------------------------

Subject: 8b.9   Presta Valve Nuts
From:  Jobst Brandt <[e-mail]>
Date:    Fri, 07 Nov 1997 16:46:59 PST

Jam nuts on Presta valve stems and pumping.

1. The jam nut holds the stem when pumping so that it does not recede
   into the rim when pressing the pump head against the tire.  This is
   especially useful when the tire is flat (after installing the
   tube).  It also keeps the stem from wiggling around while pumping.
   Removing the nut should present no difficulty unless the threads
   have been damaged or the hands are cold.  The cold may present a
   problem, but then just opening the valve nut on a Presta valve
   under such conditions is difficult.

2. Breaking off stems with a frame pump comes from incorrect pumping.
   The number of new tubes with broken stems lying along the road
   proves that this occurs far too often.  To avoid breaking the stem,
   the pump head should be be held in the fist so that the pumping
   force goes from one hand into the other, not from the pump into the
   valve stem.  To practice the correct action, hold the pump head in
   one hand with the thumb over the outlet, and pump vigorously
   letting out no air.  All the force goes from one hand into the
   other.  This is essentially what should take place when inflating a
   tire.

   It does no good to "get even" with the stupid tube by discarding it
   on the road for all to see.  Most riders understand how to pump a
   tire and see this only as evidence of incompetence rather than a
   faulty tube.  Besides, this ostentatious behavior constitutes
   littering for which the the fine in California is $1000.  Bike
   shops should instruct new bike owners about the use of the frame
   pump.  Along with this there should be some tire patch hints like
   don't try to ride a freshly patched tube, carry a spare tube and
   always use the spare after patching the punctured tube.  Of course
   this is a whole subject in itself that is also treated in the FAQ.

------------------------------

Subject: 8b.10   Rim Tape Summary
From: Ron Larson <[e-mail]>

This is a summary of the experience of riders on the net regarding
various rim tapes, both commercial and improvized. Any additional
comments and inputs are welcome.

RIM TAPE

Rim tape or rim strips are the material that is placed inside a
clincher rim to protect the tube from sharp edges of the nipple holes
and possibly exposed ends of spokes extending beyond the nipples. Many
materials have been used to produce rim tapes: plastic, rubber, tapes
consisting of a multi-directional fiber weave, duct tape and fiberglass
packing tape.

A few factors influence how well a rim tape works. Some of the tapes
are available in more than one width. It is important to choose the
width that provides the best fit to cover the entire "floor" of the rim
as opposed to a tape that is barely wide enough to cover the nipple
holes. Another factor is how well the rim tape withstands the stress of
being stretched over the nipple holes with a high preassure inner tube
applying preassure to it. The main form of failure of the plastic tapes
is for the tape to split lengthwise (in the direction the tube lies in
the rim) under high preassure forming a sharp edge that the tube
squeezes through and then rubs against. Thus the splitting tape causes
the flat that it was supposed to be protecting against.

REVIEW OF RIM TAPES BY TYPE

Plastic Tapes

Advantages:

Easy to install and remove. No sticky side is involved.

Disadvantages:

Although there are exceptions, they are prone to splitting under
preassure.

Michelin                      Good Experiences: 0  Bad Experiences: 6

Cool Tape                     Good Experiences: 2  Bad Experiences: 0

  Cool Tape is thicker than other plastic tapes and does not exhibit
  the splitting failure noted above.

Hutchinson                    Good Experiences: 0  Bad Experiences: 2

Specialized                   Good Experiences: 1  Bad Experiences: 4

Rubber Tapes

Advantages:

Easy to install and remove. Good if the nipples are even with the rim
floor and there are no exposed spoke ends.

Disadvantages:

Stretch too easily and allow exposed nipple ends to rub through the
tape and then through the tape.

Rubber strips                 Good Experiences: 0  Bad Experiences: 2

Cloth tapes woven of multi-directional fibers:

Advantages:

Easy to install. Do not fail under preassure.

Disadvantages:

They are a sticky tape and care must be taken not to pick up dirt if
they need to be removed and re-installed.

Velox                         Good Experiences:11  Bad Experiences: 0

  Velox rim tape comes in three different widths. Be sure to get the
  widest tape that covers the floor of the rim without extending up the
  walls of the rim.  The stem hole may need to be enlarged to allow the
  stem to seat properly. Otherwise the stem may push back into the tube
  under preassure and cause a puncture at the base of the stem.

Non-commercial rim tapes

Fiberglass packing tape (1 or 2 layers)

Advantages:

Cheap. Readily available. Easy to install.

Disadvantages:

Impossible to remove. If access to the nipples is required, the tape
must be split and then either removed and replaced or taped over.

Fiberglass packing tape       Good Experiences: 1  Bad Experiences: 1

Duct tape (hey, someone tried it!!)

Advantages:

CHEAP. Readily available.

Disadvantages:

Useless. Becomes a gooey mess that is impossible to remove.

Duct tape                     Good Experiences: 0  Bad Experiences: 1

CONCLUSION

While plastic tapes are easy to work with, they often fail. The clear
winner in this survey is the Velox woven cloth tape. A quick review of
mail order catalogs confirms the experiences of the net. Velox was
available in 5 out of 5 catalogs checked.  It was the only rim tape
available in 3 of the catalogs. The other 2 had one or two plastic
tapes available. (None sold duct tape...)

One good suggestion was a preassure rating for rim tapes much like the
preassure rating of tires.

------------------------------

Subject: 8b.11   Talcum Powder for Tubes and Tires
From:  Jobst Brandt <[e-mail]>
Date:    Tue, 04 Nov 1997 16:54:17 PST

> I've been told since my first bike that I should liberally dust the
> tube in talcum powder before installing it.  I've believe that this
> may have reduced the number of flats I've had recently.

Talcum is one of the more durable urban legends.  There is no benefit
in putting talcum or substitute powder on a tube or in a tire.  The
practice has come to bicycle tires the same way tire treads that are
miniature replicas of automobile treads have... if it's good for cars,
it must be good for bicycles.  Trucks (and formerly cars) use talcum
or graphite powder between tire and tube, because without it, the two
can vulcanize from the heat of rolling.  This often makes tube removal
destructive, leaving tube fragments stuck in the tire casing.

Bicycles do not generate enough heat to vulcanize tubes, so they can
be removed from the tire without problem.  Other than that, talcum has
no effect on punctures other than to release air faster when one
occurs.  A tube stuck to the casing will retain air for a considerable
distance after a thorn penetration because the thorn that penetrates
plugs the casing hole leaving the tube hole with no outlet.  This is
especially true for snake bites.  I have found such flats the day
after when they have gone flat over night.  Without powder, a tube
will stick adequately to most clincher tires in about 100 miles.

Corn starch is no better than talcum powder, the only difference being
that it is water soluble, but then who cares.  Talcum also cakes up
when wet, although it doesn't dissolve.

A tube cannot move in a tire when inflated, regardless of what powder
is used, because, no translational forces exist, on top of which the
holding force between tube and casing is large.  That talcum prevents
damage when mounting a tire is also not the case, because the pinch
occurs when the last part of the bead is being popped onto the rim.
This can cause a pinch with or without a tire iron, and powder will
not protect a tube from lying in the gap if it hasn't been pushed into
the tire adequately.

The reason tubes have talcum powder inside is that in manufacture,
they become hot enough that, otherwise, they could become inseparably
stuck when folded.  That is why most butyl tubes have talcum inside.

------------------------------

Subject: 8b.12   ETRTO numbers for tire sizes
From: Osman Isvan <[e-mail] >

There is nothing wrong with tire/rim compatibility. If
we...stop calling them with colloquial names such as "26 inch
wheel", "road wheel", etc., we would be all set.

There is no dimension on a mountain bike rim that is even
close to 26 inches. The ETRTO number, bead diameter in
millimeters, is *molded* on the sidewall of the tire (to make
mislabeling almost impossible) and if it matches, it will
match. There is nothing confusing, mysterious or misleading or
complicated about the ETRTO designation. The ETRTO designation
also includes the width of the tire to be sure it is not too
narrow or too wide for the rim, but this dimension is not
accurate as it is not critical.

Common standard bead diameters are 559 mm (ATB), 571 mm
(Triathlon) and 622 mm (road). They are a reasonable size
smaller/larger than each other, so what's the problem?

The confusion comes from us (marketers and consumers)
referring to both the 559 and the 571 standards, and a slew of
others, as 26" for some reason. The term "26 inch wheel"
refers to the approximate outside diameter of the inflated
tire, and has nothing to do with tire/rim compatibility...

This is no different with cars, but in automotive "lingo" the
colloquial names for wheel sizes are the rim diameter (and
that's what matters for compatibility), not the tire outside
diameter. The same car comes with either "13 inch" or "14
inch" wheel options but the outside diameter of the tire may
be the same. The rubber part takes up the difference.
Motorists refer to their RIM SIZE when they talk about wheel
diameter. A 13 inch tire such as "175/70 R 13" means it will
fit to a 13 inch rim.

We should do the same. It is possible to build the same
outside diameter by either using a 26 mm wide tire and 559 mm
(mountain) rim (ETRTO 26-559) or a 20 mm wide tire on a 571mm
(triathlon) rim (ETRTO 20-571), and this doesn't imply they
would be interchangeable. And because the 559 mm (Mountain)
rims have a diameter of only 22 inches, it takes very fat 2.0
inch (Mountain) tires to bump them up to 26". Of course they
wouldn't accept skinny triathlon tires of same thread
diameter.

When ordering tires, order according to bead diameter (ETRTO
designation). This will solve any problems with compatibility.
If the salesperson doesn't understand, ask to look for the
number which is molded with the casing.

------------------------------

Subject: 8b.13   Tires with smooth tread
From:  Jobst Brandt <[e-mail]>
Date:    Fri, 05 Dec 1997 16:29:59 PST

Drag racers first recognized the traction benefits of slick tires,
whose benefit they could readily verify by elapsed times for the
standing start quarter mile.  In spite of compelling evidence of
improved traction, more than twenty years passed before slicks were
commonly used for racing cars, and another twenty before they reached
racing motorcycles.  Today, slicks are used in all weather by most
street motorcycles.  In spite of this, here at the end of the
millennium, 100 years after John Dunlop invented the pneumatic tire
for his own bicycle, bicyclists have not yet accepted smooth tread.

Commercial aircraft, and especially motorcycles, demonstrate that a
round cross section tire, like the bicycle tire, has an ideal shape to
prevent hydroplaning.  The contact patch, a pointed canoe shape,
displaces water exceptionally well.  In spite of this, hydroplaning
seems to be a primary concern for riders who are afraid to use smooth
tires.  After assurances from motorcycle and aircraft examples,
slipperiness on wet pavement appears as the next hurdle.

Benefits of smooth tread are not easily demonstrated because most
bicycle riders seldom ride near the limit of traction in either curves
or braking.  There is no simple measure of elapsed time or lean angle
that clearly demonstrates any advantage, partly because skill among
riders varies greatly.  However, machines that measure traction show
that smooth tires corner better on both wet and dry pavement.  In such
tests, other things being equal, smooth tires achieve greater lean
angles while having lower rolling resistance.

Tread patterns have no effect on surfaces in which they leave no
impression.  That is to say, if the road is harder than the tire, a
tread pattern does not improve traction.  That smooth tires have
better dry traction is probably accepted by most bicyclists, but wet
pavement still appears to raise doubts even though motorcycles have
shown that tread patterns do not improve wet traction.

A window-cleaning squeegee demonstrates this effect well.  Even with a
new sharp edge, it glides effortlessly over wet glass leaving a
microscopic layer of water behind to evaporate.  On a second swipe,
the squeegee sticks to the dry glass.  This example should make
apparent that the lubricating water layer cannot be removed by tire
tread, and that only the micro-grit of the road surface can penetrate
this layer to give traction.  For this reason, metal plates, paint
stripes, and railway tracks are incorrigibly slippery.

Besides having better wet and dry traction, smooth tread also has
lower rolling resistance, because its rubber does not deform into
tread voids.  Rubber being essentially incompressible, deforms like a
water filled balloon, changing shape, but not volume.  For a tire with
tread voids, its rubber bulges under load and rebounds with less force
than the deforming force.  This internal damping causes the energy
losses of rolling resistance.  In contrast the smooth tread transmits
the load to the loss-free pneumatic compliance of the tire.

In curves, tread features squirm to allow walking and ultimately,
early breakout.  This is best demonstrated on knobby MTB tires, some
of which track so poorly that they are difficult to ride no-hands.

Although knobby wheelbarrow tires serves only to trap dirt, smooth
tires may yet be accepted there sooner than for bicycles.

------------------------------

Subject: 8b.14   Rolling resistance of Tires
From:  Jobst Brandt <[e-mail]>
Date:    Thu, 08 Aug 1996 17:17:57 PDT

The question often arises whether a small cross section tire has lower
rolling resistance than a larger one.  The answer, as often, is yes
and no, because unseen factors come into play.  Rolling resistance of
a tire arises almost entirely from flexural rubber losses in the tire
and tube.  Rubber, especially with carbon black, as is commonly used in
tires, is a high loss material.  On the other hand rubber without
carbon black although having lower losses, wears rapidly and has
miserable traction when wet.

Besides the tread, the tube of an inflated tire is so firmly pressed
against the casing that it, in effect, becomes an internal tread.
The tread and the tube together absorb the majority of the energy lost
in the rolling tire while the inter-cord binder (usually rubber) comes
in far behind.  Tread scuffing on the road is even less significant.

Patterned treads measurably increase rolling resistance over slicks,
because the rubber bulges and deforms into tread voids when pressed
against the road.  This effect, tread squirm, is mostly absent with
smooth tires because it cannot be bulge laterally by road contact
because rubber, although elastic, is incompressible.

Small cross section tires experience more deformation than a large
cross section tire and therefore, should have greater rolling
resistance, but they generally do not, because large and small cross
section tires are not identical in other respects.  Large tires nearly
always have thicker tread and often use heavier tubes, besides having
thicker casings.  For these reasons, smaller tire usually have lower
rolling resistance rather than from the smaller contact patch to which
it is often attributed.

These comparative values were measured on various tires over a range
of inflation pressures that were used to determine the response to
inflation.  Cheap heavy tires gave the greatest improvement in rolling
resistance with increased pressure but were never as low as high
performance tires.  High performance tires with thin sidewalls and
high TPI (threads per inch) were low in rolling resistance and
improved little with increasing inflation pressure.

As was mentioned in another item, tubular tires, although having lower
tire losses, performed worse than equivalent clincher tires because
the tubular's rim glue absorbs a constant amount of energy regardless
of inflation pressure.  Only (hard) track glue absolves tubulars of
this deficit and should always be used in timed record events.

------------------------------

Subject: 8b.15   Wiping Tires
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 13 Oct 1997 15:02:23 PDT

Although the tire wiping has mostly gone the way of the tubular tire,
some riders have remained believers in this practice, that never had
any validity in the first place.  It is purportedly done to prevent
punctures by wiping off glass that may have "stuck" to the tire.

If one considers the rotation rate of a wheel in typical bicycling,
about 15-20mph, it comes to about 3.5 revolutions per second.  When
observing a tire wiper, the time between noticing hazardous debris on
the road and the first wipe is more than a second.  Hence, any glass
or other small object would be firmly pressed into the tire by four
revolutions and all exposed glass edges chipped off.  By the time the
other tire is wiped several more seconds will have passed.  If the
glass is not thoroughly embedded by then it will not enter the tire.

This is not to say that particles embedded in a tire always cause a
leak immediately, but that they are irrecoverably in the tire at that
time.  Those who have patched flats from glass will recall that the
piece of glass is not easily found, especially if the location of the
puncture is not known.  The embedded chip is usually imperceptible
when wiping the hand over the place even when known.

On the other hand, the rear wheel is more subject to flats than the
front, because flat objects must first be tipped up to engage a tire
to have any effect.  Wiping the rear tire on common short frame
bicycles is hazardous, because the fingers can be sucked into the
narrow gap between tire and seat tube to cause serious injury.

Carefully considered, tire wiping is an idle gesture, reassuring to
some riders, and impressive to others if deftly executed.  I recall as
a beginner that learning all the tics of bicycle racing was important.
Wiping tires was one of these.  Forget it.

------------------------------

Subject: 8b.17   Clinchers vs. Tubulars
From: F.J. Brown <[e-mail]>

[e-mail] gave some useful hints on mounting clinchers,
mostly involving the use of copious quantities of baby powder, and
trying to convince me that clinchers aren't difficult to mount, so ease of
mounting isn't a valid reason for preferring tubulars.

[e-mail] wrote that although average tubulars ride
'nicer' than average clinchers, there are some clinchers around that ride
just as 'nice'.   He also said that ease of change isn't a good reason for
preferring tubulars as if you flat in a race, you're either going to swap
a wheel or drop out.   He pointed out that tubulars end up costing $20 -
$80 per flat.

[e-mail] gave some of the historic reasons that tubulars were
preferred: higher pressures, lower weight, stronger, lighter rims.   Said
that only a few of these still hold true (rim strength/weight, total weight),
but he still prefers the 'feel' of tubulars.

[e-mail] started this thread with his observations on
clinchers seperated from their rims in the aftermath of a race crash.

[e-mail] comments on improperly-glued tubulars posing a threat
to other racers by rolling off, and noted that this couldn't happen with
clinchers.

[e-mail] agreed with stek, with the additional note that
it is inadequate inflation that often allows tubulars to roll.

Kevin at Buffalo agreed with stek and jobst about tubulars (improperly or
freshly glued) sometimes rolling.

[e-mail] says he uses clinchers for cost and convenience.
Clinchers let him carry around a tiny patch kit and some tyre irons, costing
60c, whereas tubulars would require him to carry a whole tyre, and would
cost more.

CONCLUSIONS: THE CLINCHER VS. TUBULAR WAR
Tubulars - used to be capable of taking higher pressures, had lower weight
           and mounted onto stronger, lighter rims than clinchers.   Clinchers
           have now largely caught up, but many cyclists thinking hasn't.
           Tubular tyre + rim combination still lighter and stronger.
         - are easier to change than clinchers.   This matters more to some
           people than others - triathletes, mechanical morons and those
           riding in unsupported races.
         - cost megabucks if you replace them every time you puncture.
           ***However*** (and none of the North Americans mentioned this)
           down here in Kiwiland, we ***always*** repair our punctured
           tubulars (unless the casing is cut to ribbons).   The process
           doesn't take much imagination, you just unstitch the case, repair
           the tube in the normal manner using the thinnest patches you can
           buy, stitch it back up again and (the secret to success) put a
           drop of Superglue over the hole in the tread.
         - can roll off if improperly glued or inflated.   In this case, you
           probably deserve what you get.   Unfortunately, the riders behind
           you don't.

Clinchers - can be difficult to change (for mechanical morons) and are always
            slower to change than tubulars.   Most people still carry a spare
            tube and do their repairs when they get home.
          - are cheaper to run: if you puncture a lot clinchers will probably
            still save you money over tubulars, even if you repair your
            tubulars whenever possible.   Tubulars are only repairable most
            of the time, you virtually never write off a clincher casing due
            to a puncture.
          - have improved immensely in recent years; top models now inflate
            to high pressures, and are lighter and stronger than they used
            to be.   Likewise clincher rims.   Some debate over whether
            tubulars are still lighter and tubular rims stronger.   Probably
            depends on quality you select.   No doubt that high quality
            clinchers/rims stronger, lighter and mor dependable than cheap
            tubular/rim combination.

------------------------------

Subject: 8b.18   Tubular Fables
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 27 Jan 2003 20:38:07 -0800 (PST)

> Why is it better to deflate tubulars between rides or is this just a
> silly rumor?

Yes and no.  The "rumor" arises from a misunderstanding.  Track tires,
that are most often still tubulars, are generally inflated to more
than 10 bar and are dangerous if they were to explode.  Good track
tires, unlike road tires, are often made of silk with fine and thin
strands that are not coated or otherwise protected.

I have seen these tires get touched by another rider's pedal and
explode, or even when carelessly laid on any angular object, they can
burst because only breaking a few cords is enough to start a burst.
For this reason track tires are best deflated to less than half their
running pressure when not in use.  I can still vividly hear the sound
of a tire exploding in an indoor track although I heard it only a few
times years ago.  It is not something you would like to have happen in
your car or room.

The reasons people give for deflating tubulars are generally false and
are given for lack of understanding.  This is what makes it sound like
an old wive's tale.  Most people do it just to be doing what they
think is "professional" when in fact the protected sidewalls and
pressure of most road tubulars makes deflation as meaningless for them
as it is for clinchers.

> What advantage is there in aging tubulars?

None!  The aging concept arose from the same source as the "steel
frames need to be replaced because they get soft with age" concept.
Both were intended to improve sales during the off (winter) season by
bike shops with too much inventory on their shelves.  Tires oxidize,
outgas, and polymerize from ultraviolet light.  The concept of a tire
manufacturer making a tire that cannot be used until ripened for six
months from the date of purchase is ridiculous.  Tires can be made to
any specification at the factory.  Tires are most flexible and durable
when they are new.  They don't improve with time and exposure to heat,
light, and oxygen or ozone.

"Over-aged" tubular tires, have crumbling hard brown latex on their
sidewalls that exposes separating cords directly to weather and wear
and they have treads crack when flexed.  Considering that this is a
continuous process, it is hard to explain where, in the time from
manufacture to the crumbly condition, the optimum age lies.  The claim
that tires are lighter after aging is true.  Their elastomers have
evaporated making the tire brittle and weak.

Purchasing tubular tires in advance to age them is unwise, although if
there is a supply problem, tubular tires bought in advance should be
sealed tightly in airtight bags and kept in the dark, optimally in a
freezer.  For best results, use new tires because aged tires are only
as good as how little they have aged.

------------------------------

Subject: 8b.19   Tubular Tire Repair
From:  Jobst Brandt <[e-mail]>
Date:    Tue, 04 May 1999 11:07:38 PDT

Opening the Tire

The tire casing must be opened to gain access to patch the tube.  To
do this, open the casing by peeling the base tape back and unstitching
the seam.  If this is a seamless tire, chuck it.  There are two types
of seams, zipper stitch (using one thread) and two thread stitch.  The
zipper stitch is identified by having only one thread.  It appears to
make a pattern of slanted arrows that point in the direction in which
it can be 'unzipped'.

Never open more tire than is necessary to pull the tube out of the
casing.  Remember, the tube is elastic and can be pulled a long way
from a three cm long opening.  Even if there are two punctures not too
far apart, the tube can be pulled out of a nearby opening.  However,
to insert a boot requires an opening of about 6 to 10 cm at the
location of the cut or rupture, about the length of the boot (at least
10cm) and a couple of cm more.

Base Tape

Never cut the base tape because it cannot be butt joined.  Always pull
it to one side or separate it where it is overlapped.  Do not cut the
stitching, because it takes more time to pull out the cut thread than
to pull it out in one piece.  When working on the stem, only unstitch
on one side of the stem, preferably the side where machine finished.
Use latex to glue down loose threads on a sidewall cut.  Paint the
exposed casing zone that is to be covered by the base tape and the
tape with latex emulsion, allow to partially dry and put the tape in
place.  Put the tire on a rim and inflate hard.

Seam Ripper and Triangular Needle

A convenient tool, available in the sewing department at most
department and sewing specialty stores is a seam ripper.  This and the
triangular sewing needle from a Velox patch kit are two highly useful
tools for tubular repair, scissors and razor blades being common
household items.

Zipper Stitch

Cut the thread at some convenient place at the upstream end of the
intended opening and with a blunt awl, like a knitting needle, pull
out several stitches in the direction the stitch pattern points.  When
enough thread is free to pull on, the stitching can be opened like a
zipper.  When enough seam is open, thread the loose end through the
last loop and pull tight, to lock the zipper.  Don't cut off the free
end because it is often good enough to re-sew the seam.

Two Thread Stitch

One of the threads makes a zig zag as it locks the other thread where
it penetrates the tire casing.  Cut both threads near the middle of
the opening and, with a blunt awl like a knitting needle, pull out
only the locking thread in both directions, stitch at a time.  The
locking thread is the one that is easier to pull out.  Remove as many
stitches as the opening requires.  The other thread pulls out like a
zipper.  Tie a square knot with the loose ends at both ends of the
opening and cut off the rest.

Patching

Patch butyl (black) tubes using patches from a bicycle patch kit.

To patch a latex tube, make patches from an old latex tube that are
fully rounded and just large enough to cover the hole plus five mm.
For instance, a thorn hole takes a 10 mm diameter patch.  Use Pastali
rim glue (tire patch glue also works but not as well) wiped thinly
onto the patch with your finger.  Place the patch on the tube
immediately and press flat.  Latex will pass the volatile solvent
allowing the glue to cure rapidly with good adhesion to the tube.

Casing Repair

Repairing tubular tires requires latex emulsion.  You can get it from
carpet layers, who usually have it in bulk.  You must have a container
and beg for a serving.  If you are repairing a tubular you probably
ride them, and therefore, will have dead ones lying around.  The best
tubulars generally furnish the best repair material.

Most cuts of more than a few cords, like a glass cut, require a
structural boot.  With thin latex tubes, uncovered casing cuts will
soon nibble through the tube and cause another flat.  For boot
material, pull the tread off a silk sprint tire, unstitch it and cut
off the bead at the edge of the fold.  Now you have a long ribbon of
fine boot material.  Cut off a 10cm long piece and trim it to a width
that just fits inside the casing of the tire to be booted from inside
edge of the bead (the folded part) to the other edge.

The boot must be trimmed using a razor blade to a thin feathered edge
so that the tube is not exposed to a step at the boot's edge,
otherwise this will wear pinholes in a thin latex tube.  Apply latex
to the cleaner side of the boot and the area inside the tire,
preferably so the boot cords are 90 degrees from the facing tire
cords.

Insert the boot and press it into place, preferably in the natural
curve of the tire.  This makes the the boot the principal structural
support when the tire is again inflated, after the boot cures.  If the
casing is flat when the boot is glued, it will stretch the casing more
than the boot upon inflation.  After the boot dries, and this goes
rapidly, sew the tire.

Valve Stem Replacement

This depends on the type of tube.  Latex tubes and some of the others
have a screwed in stem that has a mushroomed end on the inside and a
washer and nut on the outside.  These are easily replaced from another
tire whose tube is shot.  Open the old ruined tire at the stem, loosen
the nut, lift the washer and pull out the stem.

Open the tire to be repaired on one side of the stem, preferably the
side where sewing ended, the messier side, and loosen the base nut,
lift the washer, wet the stem at the tube opening with saliva and
twist it until it turns freely.  Pull it out carefully and insert the
replacement stem after wetting its mushroom with saliva.  Tire
stores have a soapy mixture called "Ru-glide" or the like to do the
wetting but it cost a lot more than spit and doesn't work any better.

Tube Replacement

To replace the entire tube, open the tire on one side of the stem, the
side that seems to be easier to re-sew after the repair.  Open about
eight to ten cm the usual way, so that the old tube can be pulled out
by the stem.  Cut the tube and attach a strong cord to the loose end
of the tube to be pulled through the casing by the old tube as you
pull it out.

Cut the "new" latex tube about 8-10 cm away from the stem, tie the
cord onto the loose end and pull it gently into the casing.  Dumping
some talc into the casing and putting talc onto the tube helps get the
tube into place.  With the tube in place, pull enough of it out by
stretching it, to splice the ends together.

Splicing the Tube

This procedure works only with latex tubes.  Overlap the tube ends so
the free end goes about one cm inside the end with the stem.  With the
tube overlapped, use a toothpick to wipe Pastali rim cement into the
interface.  The reason this MUST be done in place is that the solvent
will curl the rubber into an unmanageable mess if you try this in free
space.  Carefully glue the entire circumference and press the joint
together by pressing the tube flat in opposing directions.  Wait a
minute and then gently inflate to check the results.  More glue can be
inserted if necessary if you do not wait too long.

Sewing the Tire

Sewing machines make holes through the bead that are straight across
at a regular stitch interval.  For best results, use the original
stitch holes when re-sewing.  Use a strong thread (one that you cannot
tear by hand) and a (triangular) needle from a Velox tubular patch kit
(yes I know they are scarce).  Make the first stitch about one stitch
behind the last remaining machine stitch and tie it off with a noose
knot.

With the beads of the tire pressed against each other so that the old
holes are exactly aligned, sew using a loop stitch pulling each stitch
tight, going forward two holes then back one, forward two, back one,
until the seam is closed.  This is a balanced stitch that uses one
thread and can stretch longitudinally.

Gluing Tire to Rim

For road tires, that are intended to be manually mounted and replaced
on the road, tires with a rubberized base tape are preferred because
these are easily and securely mounted by applying a coating of glue to
the rim, allowing it to harden and mounting the tire to be inflated
hard so that it will sink in and set.

Because road tires are intended to be changed on the road, they use a
glue that does not completely harden and allows reuse for mounting a
spare.

Track tires, in contrast can be mounted using hardening glue such as
shellac or bicycle tire track glue.  This glue is best suited for base
tapes that are "dry" cloth.  The tire is mounted either with a light
coating of track glue on the base tape or un-glued onto a good base of
track glue whose last coat is still soft on the rim, into which the
tire will set when inflated upon mounting.  Hard glue prevents rolling
resistance otherwise generated by the gummy road glue.  Track glue is
primarily useful for record attempts where every effort is needed.

Mounting a Tubular

The most effective and fastest way to mount a tubular is to place the
rim upright on the ground, stem hole up; insert the valve stem of the
tire and with both hands stretch the tire with downward force to
either side, working the hands downward to the bottom of the rim
without allowing the tire to slacken.  Try this before applying rim
glue on a dry rim and inflate the tire hard so that afterward,
mounting is easier on the glued rim.

Note that inflation pressure causes the tire to constrict until the
cord plies are at about 35 degrees.  This effect helps retain the tire
on the rim in use.  Therefore, do not inflate a tire to mount it.
Tubulars should generally not be inflated off a rim because this
deforms the tire and base tape adversely, possibly shearing the
inter-ply adhesion and loosening the base tape and stitching.

Now that you know everything there is to know about this, get some
practice.  It works, I did it for years.

------------------------------

Subject: 8b.20   Gluing Sew-up Tires
From: Roger Marquis <[e-mail]>

[More up to date copies of Roger's articles can be found at
 http://www.roble.com/marquis/]

 Davis criterium, it's hot, hot, hot.  The pace is fast and the
corners sharp.  Inevitably some riders are going to roll tires,
happens every year.  What can you do to insure that your sew-up
tires stay glued when the mercury rises?

There is no one cause of poor tire-rim adhesion so let's start at
the beginning, new rims and tires.  Most rims are shipped with a
coating of anti-corrosive substances that closely resemble grease.
This has to be thoroughly removed with solvent and a clean rag
before you can put down the first coat of glue.  Fast Tack is not
the best glue to use on a bare rim.  Instead try Clement, Wolber or
one of the other slower drying glues.  Put a thin coat of glue all
the way around and leave the wheel(s) to dry for at least 12 hours.

 While this glue is drying you might check your tires for any latex
that might be covering the base tape.  If there is any latex at all
give it a good roughing up with coarse sandpaper before coating it
with a thin layer of standard glue or Fast Tack.  This too should
be left to dry for a few hours.  If you're a light rider or don't
plan on doing any hard cornering on hot days you can usually leave
out this step but always roughen the latex on the base tape.

 After the base coat of glue has dried it's time for the adhesive
layer.  This should be thicker than the first layer but not so
thick that it can squeeze out from under the tire when you mount it
and get on the rim and sidewalls.  If you are using a traditional
style road glue let it dry for ten to fifteen minutes before
putting your tires on.  Tires should be mounted on Fast Tacked rims
immediately.

 New tires usually need a good stretching before they will go onto
the rim without tending to roll and get glue all over them.  I
usually stretch a tire by pulling it around my knees and feet for
a few seconds and then mounting it on an old rim for a while.  You
might want to try mounting the tire on a dry rim first to see just
how much stretching it will need.

 If you used traditional sew-up glue you should wait at least 12
hours before doing any serious cornering.  If you need to race
right away you can use Fast Tack and corner confidently within an
hour.  Be sure to spread the glue evenly over the surface of the
rim using your finger or a brush.  To get the last section of tire
onto the rim without making a mess grab the remaining 3 or 4 inches
and lift the tire away from and over the rim.  This can be
difficult if you forget to stretch it beforehand.

 Some glues work better than others in hot weather.  Fast Tack works
best followed by Wolber and Vittoria with Clement in the middle and
Tubasti at the bottom of the list.

 When buying Fast Tack be sure you get the real thing.  3-M sells
other trim adhesives in boxes nearly identical to Fast Tack.  These
trim adhesives do not work for bicycle tires!  Be careful that
whatever glue you do use has not separated in its tube.  If it has,
take a spoke and stir it up before you squeeze it out.  I have also
heard of mixing different glues before application.  This is a
dangerous shortcut that yields unpredictable results.  Fast Tack
and Clement are the most popular tire adhesives.  Even though Fast
Tack will dry out you can get a few tire changes between
replications if you have a good layer of traditional glue on the
rim underneath it.  Racing tires though, should be reglued each
time.  Base tapes can come apart from the tire in hot weather and
underinflation can cause tires to roll as well.  Check these things
as well as the tread for wear or cuts before every race and you'll
be able to descend and corner with confidence.

Roger Marquis ([e-mail])

------------------------------

Subject: 8b.21   Another way to glue sewup tires
From:    "Mike & Joanna Brown" <[e-mail]>
Date:    Wed, 06 May 1998 21:49:53 CDT

I have been racing for 6 years now and have tried multiple tire/rim
combinations.  I have come to the conclusion that good tubular tires on a
pair of good carbon fiber rims provide the ultimate ride.  But many people
dislike tubular tires because of the gluing process and the possibility of
rolling the tire during fast cornering.

I decided to write this article because of the three to four racers who
rolled a tire at the recent Baylor/Mirage sponsored criterium.  Rolling a
tire at anytime during race can be catastrophic.  Everyone has their "best"
way of gluing a tire.  I can assure you, this is by far the best and SAFEST
way to glue a tire to prevent it from rolling during any type of cornering
at any speed.  I took this process out of Cycling USA last year and now
follow it religiously when gluing my own tires.  This gluing process was
far superior to the manufacturers recommended process in regards to bond
strength at tire/rim interface.  We will briefly discuss the following; 1)
The glue 2) Mounting tubulars to new rims 3) Mounting tubulars to used
rims.

Not all glues are the same.  Especially in Texas!  The temperature outside
may be 90 to 100 degrees, but the surface you are racing on may be 150 to
160 degrees.  You definitely want a glue that sets up hard in hot weather.
If not, as the temperature increases the glue/bond gets softer/weaker and
chances of roll off and serious injury increase.  The article listed seven
glues in this order of strongest to weakest tire/rim bond; Vittoria Mastik'
One, Continental, Wolbar, SM Fast Track, Vittoria Gutta, Pana Cement and
Clement.   I prefer clear glues.  That way if you screw up its very
difficult to tell.  With colored glues, if you screw up everyone knows.
Also for your information I use Pana Cement.  It does not provide the
strongest bond, but it sets up perfectly in all extremes of hot weather and
it takes one hell of a finger bleeding effort to get the tire off the rim.

Gluing tubulars to new rims properly should take about 84 hours.  Here's
the process.  Test mount the tubular to a dry rim, inflate to 100 psi and
allow to sit 24 hours.  This stretches the tire which will make mounting
easier and also allow you to inspect the tube and tire for defects (most
"good" tubulars are hand made).  After 24 hours remove the tire.  Clean the
rim with acetone, lacquer thinner or alcohol only.  Other types of cleaners
may leave a film on the rim that cannot be seen by the eye and will
decrease tire/rim bond strength.  Composite rim owners should contact the
manufacturer for recommended solvents.  Roughing the rim surface will not
improve the bond strength.  Gently scrap the base tape on the tire with a
straight edge to remove any latex.  If you scrap a one inch section and the
appearance of the base tape does not change, then you probably have no
latex on the base tape and can stop scrapping.  But be sure to visually
inspect the entire base tape just to be sure.

Inflate your tire off the rim until the base tape rolls outward.  Apply a
uniform layer of glue over the entire base tape area.  It is best to do
several tires at this time.  You can store those tires not used and
anticipate that the adhesive bond will remain strong as long as the tire
surface is kept clean.  Apply a uniform layer of glue across the entire
width of the tire rim gluing surface.   The principle bond is at the rim
edge; therefore, it is critical for performance to ensure that the glue
reaches the edges of the rim.  Allow both to dry for 24 hours.  Apply an
additional coat after that 24 hour period and allow that 2nd coat to dry
for 12 hours.  Apply a third coat.  This is the mounting coat.  With Pana
Cement, once the third coat is applied to the tire and rim mount the tire
immediately. (One tip I would suggest here is before putting glue on the
rim is to put black electrical tape on the entire outside edge and breaking
surfaces.  This makes for very easy cleaning after the tire is put on.
Just peal the tape away and all excess glue comes with it and leaves behind
a nice, clean breaking surface).

Place the rim vertically on a clean, smooth surface with the valve hole at
the top of the rim.  Place the valve stem through the hole and ensure that
it is properly aligned-straight through the hole (Another tipàFor those
with deep dish rims requiring valve extenders, place a small amount of
loctite on the tube valve stem threads and then screw the valve extender
on.  This will prevent any leaking at that junction once the tire is glued
on).  Grab the tire 8" away from the valve stem in both directions, pull
outward with a mighty heave and place the section of tire between your
hands on the rim.  Slide your hands down another few inches down the tire,
pull and install this section.  Once a full 180 degree section of the tire
has been mounted, turn the wheel over and place the valve stem section down
vertically on the ground.  This is the point where I have my wife hold the
section of tire I had just put on the rim with two hands at 0 and 180
degrees.  I then grab the tire at the top and turn it so the base tape is
facing up.  At this point I pull up on the tire and roll it onto the top of
the rim.  It's actually very easy with two people.

Once the tire is on the rim, it must be aligned.  Inflate the tire to
about 50 psi so it can be easily "turned" to align.  You can either align
the tire by the tread or by the base tape.  Here, I prefer to align my
tires by the base tape.  Higher quality tubulars treads will align
properly.  Lower quality tires were not necessarily made straight, so
perfect alignment may not be possible.  Once aligned, inflate the tire to
100 psi and allow to dry for preferably for 24 hours.

When gluing tubulars to used rims, do not remove the old tire until you
are ready to begin the gluing process as the old tire keeps the rim surface
clear of debris which would weaken the new tire joint.  You must find a
weak point in the joint and begin removing the old tire.  On my Zipp 440's,
I use a tire lever so I do not damage the rim surface.  On aluminum rims
you can use a flat head screw driver to make it easier.  You may glue a new
tire over the old glue on the rim unless it is not contaminated or old, if
there is too much glue on the rim or if the remaining glue covers the rim
only in spots.  If one of these conditions applies to your rim, remove the
old glue with heavy duty furniture stripper.  Apply the stripper according
to the manufactures recommendations.  I always put the stripper on and let
it sit for 30 to 45 minutes and the old glue then wipes away like butter.
DO NOT wipe the glue along the rim.  This causes the old glue and stripper
to be pushed down into the nipple holes.  Wipe across the rim in small
sections.  Once the rim is free of glue, begin the process as described
above in the article.  If  you leave the old glue on the rim, apply at
least one additional coat before installing the tire.  To the tire, apply
at least one coat and let it dry for 24 hours before putting on the
mounting coat.

In concluding, let me state once again everyone has their "best" way to
mount tubulars.  I can honestly say I have mounted and raced on tubulars
put on in 24 hours.  Those instances are far and few between though.  I
always make a 100% effort to follow the procedure written above if all
possible.  84 hours seems like a long time to wait just to mount a stupid
tire.  It all comes down to how much you value safety.  When it comes to
the safety of the other riders, not to mention the consequences of roll off
to my wife and my job, I want to be damn sure I'm as safe as I can possibly
be because I took the time to do things right!

------------------------------

Subject: 8b.22   Folding a Tubular Tire
From: [e-mail] (Jobst Brandt)
Date:    Thu, 08 Aug 1996 15:31:33 PDT

Although there are many arcane folds that people devise, it boils down
to pragmatism.  Most spares are used tubulars because those who use
them typically ride together and for a new rider someone offers a
spare that gets returned or not at some later time.  Therefore, we are
talking about a previously glued tubular and the point is to prevent
the whole tire from getting goo all over the tread and sidewalls, so
you flatten the tire against itself lengthwise with the sticky base
tape stuck to the sticky base tape.  Now you have about a 40 inch long
flat tire that when folded in half twice makes the typical wad that
riders carry under their saddles secured by a footstrap.

Footstraps being nearly extinct, I don't know what people use today,
but whatever it is, it must be tight and secure.  If it isn't, the
tire will jiggle enough to abrade the sidewalls to become a
pre-packaged blowout, to be installed when you get a flat on the road.
Don't do it.  Most spare bags sold today are not good places to put a
tubular tire because they will allow the tire to vibrate too much.

It's bad news to ride alone with one spare anyway, so you ought to
ride with other tubular riders when you go any significant distance
from appropriate tire service.  It's not like carrying a tube and
patch kit that can go until you run out of patches (you can cut
patches in half too).  The advantage of using tubulars is so marginal
that the little weight saved is best applied to track and criterium
racing where its minuscule reduction in rotational inertia can at
least be argued to have some significance.

------------------------------

Subject: 8b.23   Coiling a Wire Bead Clincher
From:  Jobst Brandt <[e-mail]>
Date:    Fri, 17 Oct 1997 10:00:05 PDT

              _____________                          _________
            */             \*                      */         \*
           */               \*                    *|           |*
          */                 \*                   *|           |*
         */                   \*                  *|           |*
        *|                     |*        _________*|__________/*
        *|                     |*      */         *|
        *|                     |*     *|          *|
push--> *|     pull & turn <-- |*     *|          *|
        *|                     |*     *|          *|
        *|                     |*      *\_________*|__________
        *|                     |*                 *|          \*
         *\                   /*                  *|           |*
          *\                 /*                   *|           |*
           *\               /*                    *|           |*
            *\_____________/*        (*)tread      *\_________/*


Holding the tire seen edge-on in front of you, pull the front half
inward while turning that part so the tread faces you, to make the
figure on the right.

Fold the side loops over one another on top of the central loop.  This
is the way band saws are coiled for storage.  The three coil pack must
be secured to prevent it from springing open again.

------------------------------

Subject: 8b.24   Measuring the circumference of a wheel
From:  Jobst Brandt <[e-mail]>

For accuracy, the speedometer wants to know how far the bicycle
travels per wheel revolution (under normal load and inflation).
Therefore, that is what must be measured, and it is commonly called
the "rollout distance".  To make this measurement, sit on the bicycle
in typical riding position next to a wall for support, and roll
forward, starting with the valve stem exactly at the bottom at a mark
on the floor.  When the stem is again exactly at the bottom, measure
the distance traveled.  Typically this distance, for a 700-28 tire at
120 lbs pressure, can be as much as 30 mm shorter under load than
rolling the unloaded wheel for one revolution.

------------------------------

Subject: 8b.25   What holds the rim off the ground?
From:  Jobst Brandt <[e-mail]>

> What forces keep the rim of a wheel with pneumatic tires off the
> ground. It obviously can't be the air pressure because that's acting
> from top as well as from below.

As has been pointed out, the casing walls pull on the rim (or its
equivalent) and thereby support the load.  The casing leaves the rim
at about a 45 degree angle, and being essentially a circular cross
section, it is in contact with the rim over its inner quarter circle.
At least this is a good representative model.  The visualization may
be simpler if a tubular tire is considered.  It makes no difference
whether the tire is held on by glue or is otherwise attaches to the
rim such as a clincher is.  Either way the tire is attached to the
rim, a relatively rigid structure.

Under load, in the ground contact zone, the tire bulges so that two
effects reduce the downward pull (increase the net upward force) of
the casing.  First, the most obvious one is that the casing pulls more
to the sides than downward (than it did in its unloaded condition);
the second is that the side wall tension is reduced.  The reduction
arises from the relationship that unit casing tension is equivalent to
inflation pressure times the radius of curvature divided by pi.  As
the curvature reduces when the tire bulges out, the casing tension
decreases correspondingly.  The inflated tire supports the rim
primarily by these two effects.

Tire pressure changes imperceptibly when the tire is loaded because
the volume does not change appreciably.  Besides, the volume change is
insignificant in small in comparison to the volume change the air has
undergone when being compressed into the tire.  In that respect, it
takes several strokes of a frame pump to increase the pressure of a
tire from 100 psi to 101.  The air has a low spring constant that acts
like a long soft spring that has been preloaded over a long stroke.
Small deflections do not change its force materially.  For convenience
car and truck tires are regularly inflated to their proper pressure
before being mounted on the vehicle.

------------------------------

Subject: 8b.26   Making a tubular tire
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 23 Dec 2002 15:04:39 PST

The tedious but simple process of hand made tubulars is not much
different from mechanized manufacture that automates many of the
steps.  Tire casings are made of two crossed layers (plies) of
side-by-side cords that are not woven as cloth.  An elastic binder
between the layers holds them together and for the high quality
tubular, that binder is latex rubber.

Fabric for tubular is made on a cylindrical drum about 2m long 20cm in
diameter, with a narrow 45 degree helical slot from end to end.  A
single layer of thread (cords) is wound onto the rotating drum from
end to end and coated with latex solution.  When dry, the unwoven
cloth is cut along the 45 degree slot with a razor to produce a 20cm
wide sheet (long trapezoid) of diagonal cords lying side-by-side at 45
degrees, held together only by the latex coating.

This band, when folded in half lengthwise, with partially cured latex
to the inside, will adhere to itself, and make a 10cm wide two ply
strip.  Both edges of this strip are sheared to a desired casing
width.  The ends of this cloth band expose single layer triangles that
exactly match each other when closed in a loop to make a seamless two
ply circular band, the tire casing.  An 8mm wide selvage, through
which the tire closure seam will be stitched, is folded, glued and
sewn along both edges of the casing.

A yellow 0.4-0.8mm wall thickness latex tube, much like rubber
tourniquets used in blood clinics, is formed into a hoop with a 10mm
lap joint.  A nickel plated brass Presta valve stem, with a 10mm
diameter, rib faced mushroom end, is inserted into a 3mm diameter hole
in the tube at its overlap and where it has been reinforced by a
20x40mm elliptical rubber with fabric backing reinforcement that
prevents extrusion when the nut is clamped.  A rib-faced washer is
placed on the protruding stem, secured by a hex nut to produce the air
seal.

After laying the tube in the casing, a 20mm wide band of soft cloth is
sewn to the inside of both edges of the channel shaped casing to
prevent the tube from chafing against the main closure seam.  The main
seam uses one of two common tire stitches.  The two thread version
appears as an "X" pattern down the middle, while the other uses a
single thread diagonal loop and lock (zipper) stitch, both kinds are
biased and can change length with the casing.  The seam is machine
sewn, beginning at the valve stem, and is manually finished when it
again reaches the stem.

A bias weave base tape with a20-30mm overlap near the position of the
stem is placed on a rim and given a coat of latex as is the tire that
is mounted on the rim and inflated.  The outside of the inflated tire
is given a coat latex to which the tread that has also been primed
with latex is applied with a little stretch.  The tire is complete.

------------------------------

Subject: 8b.27 Things to check after a flat
From:    Toby Douglass <[e-mail]>
Date:    Tue, 13 Jun 2000 14:31:16 +0100

In the last two months I've had a serious spate of rear tube punctures -
about twenty and counting now.

I wanted to detail some of the things I've learned that aren't in the FAQ.

1. It's important to get your rim tape in *the right way up*.  I had a
rubber rim tape which had an "up" face and a down face.  The down face had
two raised edges to help it stay centered in the rim.  With the down face
"up", the edges cut right into the tube and kept puncturing it.  When this
happens, the puncture is a thin slit on the underside of the tube.

2. Don't use rubber rim tape for pressures over about 60 psi - it deforms
too much and eventually the buldge your tube forms pushing into the spoke
hole will rupture - this happened to me.  When you examine the tube you'll
find little buldges which have permanently deformed the tube over the spoke
hole, and one of them will have a fairly large cut in, where the tube ruptured.

3. When you've got a new tyre and you're fitting it and a tube to a wheel,
put the tyre onto the wheel a couple of times, using tyre levers (you'll
probably have to!) to stretch the tyre a little - it'll help a lot.

4. When you've had a real puncture, and you're found a stone or somesuch
which has gone through the tyre, and you're removed the object - *look
again*.  Sometimes a shard will have seperated from the object proper and
will still be in place - when you inflate the tyre and cycle again it'll
cause another puncture.

------------------------------

Subject: 8b.28 Mounting Tubular Tires
From:  Jobst Brandt <[e-mail]>
Date:    Fri, 26 Jan 2001 01:01:01 PST

Two kinds of glue are used to secure tubulars to rims, road and track,
the latter having become uncommon.  Over the years many glues have
been available by: d'Alessandro, Clement, Continental, Michelin,
Vittoria, Wolber, Pastali, Tubasti, and others.  With the decline of
tubular use, these brands have become so scarce that riders in the USA
turned to other sources, one of which was 3M Fastack (R) that compares
favorably with the others and cures faster than most.

Road tubulars preferably should have a rubberized base tape, one
coated with latex, to improve adhesion to pressure sensitive glues.
These glues behave similar to typical sticky tapes, sticking better to
slick surfaces than cloth, so that rubberized base tapes stick better
to partially dried rim cement than to bare cloth.  Do not modify
tubular base tape with cleaning solvents because they affect rim
cement adversely.  Track tubulars, to be glued with hardening
adhesive, should have bare cloth base tapes because shellac type track
glues adhere poorly to rubberized tape.  Hardening glue is used on
track tires to avoid rolling losses typical of pressure sensitive rim
cements.

Because road tires are intended to be changed on the road, their glue
must be manually separable and reusable; it must be sticky.  However,
being gooey, it allows the tire to squirm on the rim, which causes
rolling losses independent of inflation pressure.  That road tires
move on the rim is apparent from the aluminum oxide (dark grey) that
invades rim cement during use and cloth textured wear marks from base
tape in the rim.

Mounting the Tire

Stretch the new tubular tire on an old rim, inflate hard and let stand
while applying cement to the rim on which the tire is to be mounted.
Rim cement dries fairly rapidly, some faster than others.  If this is
a low viscosity rim glue, it may require more than one coat.  Apply
additional coats when the previous one has become firm enough to not
draw strings when pressing the finger into it.

When a good coating (0.5mm) of rim glue has set enough to be firm to
the touch, deflate and remove the tire from the stretching rim and
mount it on the glued.  With the wheel standing upright on the floor,
start by inserting the valve stem into the rim and stretch the tire,
pulling down with the hands to both sides away from the stem, working
around the rim until reaching the bottom with only a short section of
tire not yet in place.  Lift the wheel and thumb the remaining section
onto the rim.  Inflate the tire enough for it to take shape, centering
it on the rim before inflating hard.

Were the glue still soft and mobile, it would get on the sidewalls
while mounting the tire.  Glue should be firm enough to not make a
mess.  Because pressure sensitive glues are also thermally sensitive,
heat from braking, while descending montians, often melts rim glue
enough to make it flow from under the tire in contrast to hard (track)
glue.  While track glue (Tipo Pista) is more cumbersome to use, it has
its benefits for heat but primarily for timed events where fractions
of a second make a difference.

Mounting track tires is done the same way as with road glue only that
it takes several coats of shellac, the last of which must not be
allowed to dry, so the bare cloth rim strip will be wet by the glue as
the tire is inflated.  Mounting the tire cleanly is more difficult and
removing the tire sometimes requires tire irons.

------------------------------
------------------------------

Subject: 8b.29 Presta vs Schrader valves
From:  Jobst Brandt <[e-mail]>
Date:    Thu, 21 Feb 2002 14:42:55 -0800 (PST)

Many valve types have come along since the invention of the pneumatic
tire but for bicycles mainly Presta and Schrader remain in use.  The
Presta valve is the more slender of the two and is slightly more
cumbersome to use, having a lock nut instead of a spring to ensure
closure.  However, these two features have kept the Presta valve in
use on many bicycles.

In the past, sports and racing bicycles used Presta valves because
they are slender and enabled racers to inflate tires with a simple
pump with attached chuck (pump head) and no hose.  Presta valves are
easier to pump than Schrader, because they have no valve spring to
overcome.  Although a valve depressor for Schrader valves could
alleviate this, it would require a check valve, impractical to house
in lightweight pump heads.

The small diameter of the Presta valve requires a smaller hole in the
rim, whose size is important for narrow rims where cross sectional
strength of is significantly reduced by a stem hole.  In narrow rims,
clincher tires also leave insufficient space between tire beads for
larger Schrader valves.

In contrast Schrader valves are more robust, universally used, and
have an easily removable core.  Spring closure makes them simpler to
use because one needs only to press the inflation chuck onto them at
an automobile service station.  For hand pumps, a screwed or lever
chuck provides the valve depressor.  The depressor not only makes
inflation easier but is necessary to read back pressure in the tire.

Although Presta valves have been made with removable cores, demand is
so small that they are uncommon.  Removable Presta cores can be
identified by two wrench flats on the coarse valve cap threads.

------------------------------

Subject: 8c  Tech Wheels

------------------------------

Subject: 8c.1   Stress Relieving Spokes
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 29 Nov 1999 17:13:28 PST

> I wonder if "stress-relieving" is entirely correct?  I see it as a
> yielding/hardening process, in which the yield load is increased by
> embedding the spoke elbow in the hub, bending the elbow to a
> different angle, etc.  When unloaded from a high load, this area of
> the spoke should be more or less elastic.

> So I think the term should be "overloading" or "hardening" -- any
> thoughts?

Yes.  It appears that the process of stress relieving is obscure to
many if not most people, because after seeming to have made it clear,
comments like the above surface.  Spokes are cold formed from wire
that is (at least DT) as hard and work hardened as it can become.
Tensioning does not further harden spokes, there being no plastic
deformation.  Besides, wire ductility is important in both forming
spokes and in use.

The coiled wire from which spokes are made is straightened by running
it first between rollers staggered in X and then in Y, the wire moving
in the Z direction.  Reverse bending acts as a degausser, having ever
diminishing excursions that affect ever shallower depths of the wire.
This stress relieves the wire while removing the curl of being shipped
in a coil.  If it had no curl, releasing its free end on the spool
would allow it to uncoil explosively into a huge birds nest.

Wire is cut into suitable lengths, the first operation being to cold
form a spoke head onto one end with one axial blow of a die, after
which the spoke is cut to a specific length before rolling the thread
and bending a 100 degree elbow.

Threads, head, and elbow, contain metal that was plastically deformed
(beyond yield) as well as metal that was elastically deformed, each
having elastic memory.  In these transitions, parts that yielded and
ones that did not conflict, each wanting to return to or stay in a
different shape.  This is why a spoke bent by hand springs back only
partially when released.

On lacing spokes into a wheel, elbows are often additionally bent
(brought to yield), thus remaining at or exceeding yield stress during
tensioning.  Threads also have internal tensile stress besides local
compressive stress at the threads.  The thread core is already in
tension from the lengthening effect of thread rolling and its stress
only increases with tensioning.

Therefore, spokes in a newly built wheel have locations where stress
is near yield, some more so than others.  Because fatigue endurance of
a metal at or near the yield stress is short, cyclic loads in such
spokes will cause failures at high stress points.  In normal use, a
wheel only unloads spokes, but with spokes near yield, even these
stress cycles readily cause fatigue failures.  Only the lightest
riders on smooth roads might be spared failures with a wheel whose
spokes have not been stress relieved.

Stress relieving to relax these high stress points is accomplished by
over-stressing them in order to erase their memory.  It is not done to
bed the spokes into the hub, as is often stated.  Bedding-in occurs
sufficiently from tension.  However, stretching spoke pairs with a
strong grasp at midspan, can momentarily increased tension by 50% to
100%.  Because spokes are usually tensioned no higher than 1/3 their
yield stress, this operation has no effect on the spoke as a whole,
affecting only the small high stress zones where spokes are near
yield.  By stretching them, these zones relax below yield by as much
as the overload.

Stress relieving with a light grasp of spoke pairs is worthless, as is
bouncing the wheel or bending it in a partially opened drawer.
Pressing axially on the hub, while supporting the rim, requires a
force larger than is manually possible but is effective for spoking
machines (except the left side rear spokes that would collapse the
rim).  Another not recommend method, is laying the wheel on the floor
and walking on it with tennis shoes, carefully stepping on each pair
of crossed spokes.  The method works but bends the rim and is
difficult to control.

It is STRESS RELIEVING!  Even though people insist on calling it
pre-stressing or seating-in.  The wheel is already prestressed when
tensioned.

Jobst Brandt      <[e-mail]>



------------------------------

Subject: 8c.2   Anodized vs. Non-anodized Rims
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 20 Apr 1998 15:31:32 PDT

Dark anodized rims were introduced a few years ago as a fashionable
alternative to shiny metal finish, possibly as a response to non
metallic composites.  Some of these rims were touted as HARD anodized
implying greater strength.  Hard anodizing of aluminum, in contrast to
cosmetic anodizing, produces a porous ceramic oxide that forms in the
surface of the metal, as much as 1/1000 inch thick, about half below
the original surface and half above.  It is not thick enough to affect
the strength of the rim but because it is so rigid, acts like a thin
coat of paint on a rubber band.  The paint will crack as the rubber
stretches before any load is carried by the rubber.  Similarly,
anodizing cracks before the aluminum carries any significant load.

Rims are made from long straight extrusions that are rolled into
helical hoops from which they are cut to length.  Rims are often
drilled and anodized before being rolled into a hoop and therefore,
the anodizing is already crazed when the rim is made.  Micro-cracks in
thick (hard) anodizing can propagate into the metal as a wheel is
loaded with every revolution to cause whole sections of the rim to
break out at its spoke sockets.  In some rims, whole sidewalls have
separated through the hollow chamber so that the spokes remained
attached to the inner hoop and the tire on the outer one.  In
contrast, colored anodizing is generally too thin to initiate cracks.

As an example, Mavic MA-2 rims have rarely cracked except on tandems,
while the identical MA-40 rims, with a relativley thin anodizing, have
cracked often.

Anodizing is also a thermal and electrical insulator.  Because heat is
generated in the brake pads and not the rim, braking energy must flow
into the rim to be dissipated to the atmosphere.  Anodizing, although
relatively thin, impedes this heat transfer and reduces braking
efficiency by raising the surface temperature of the brakes.  When
braking in wet conditions, road grit wears off anodizing on the
sidewall, an effect that improves braking.

Anodizing is not heat treatment and has no effect on the structural
properties of the aluminum.

------------------------------

Subject: 8c.3   Reusing Spokes
From:  Jobst Brandt <[e-mail]>

>I just bent my wheel and am probably going to need a new one
>built.  Can I reuse my old, 3 months, spokes in the new wheel.
>The guy at the shop gave me some mumbo jumbo about tensioning or
>something.

There is no reason why you should not reuse the spokes of your
relatively new wheel.  The reason a bike shop would not choose to do
this is that they do not know the history of your spokes and do not
want to risk their work on unknown materials.  If you are satisfied
that the spokes are good quality you should definitely use them for
you new wheel.  The spokes should, however, not be removed from the
hub because they have all taken a set peculiar to their location, be
that inside or outside spokes.  The elbows of outside spokes, for
instance, have an acute angle while the inside spokes are obtuse.

There are a few restrictions to this method, such as that new rim
must have the same effective diameter as the old, or the spokes will
be the wrong length.  The rim should also be the same "handedness"
so that the rim holes are offset in the correct direction.  This is
not a fatal problem because you can advance the rim one hole so that
there is a match.  The only problem is that the stem will not fall
between parallel spokes as it should for pumping convenience.

Take a cotton swab and dab a little oil in each spoke socket of the
new rim before you begin.  Hold the rims side by side so that the
stem holes are aligned and note whether the rim holes are staggered
in the same way.  If not line the rim up so they are.  Then unscrew
one spoke at a time, put a wipe of oil on the threads and engage it
in the new rim.  When they are all in the new rim you proceed as you
would truing any wheel.  Details of this are in a good book on
building wheels.

The reason you can reuse spokes is that their failure mode is
fatigue.  There is no other way of causing a fatigue failure than to
ride many thousand miles (if your wheel is properly built).  A crash
does not induce fatigue nor does it even raise tension in spokes
unless you get a pedal between them.  Unless a spoke has a kink that
cannot be straightened by hand, they can all be reused.

------------------------------

Subject: 8c.4   Ideal Tire Sizes
From:  Jobst Brandt <[e-mail]>

> I'm getting a custom frame built and wondered what
> people thought of using 26 inch road wheels.  Smaller
> wheels ought to be lighter and stronger.

and goes on to list advantages and disadvantages, most of which are less
that important in deciding what size to use.  What in fact brought us
the wheel size (700 or 27") that we have is better understood by the
women riders who have a hard time fitting these wheels into their small
bicycle frames.  Wheels would be larger than they are if they would fit
the average riders bike, but they don't.  So the compromise size is what
we are riding today.

> It seems to me that the most obvious reason for using 27"
> wheels is tradition, but I'm not sure the advantages make
> it worth trying to swim upstream.  What do you think?

This line of thought is consistent with the "cost be damned" approach
in bicycling today.  The big bucks are spent by people who want the best
or even better than their peers.  The more special the better.  Riders
consistently spend nearly twice the money for wheels and get worse rims
when they choose anodized ones, whether there is merit to this finish
is of no interest.  They cost more so they must be better.  How "custom"
can you get than to have wheels no one else on the block has (maybe 25"?).

If enough riders ask for 24", 25" and 26" wheels, manufacturers will up
the price as their product lines multiply and the total sales remain
constant.  Tires and spokes will follow as a whole range of sizes that
were not previously stocked become part of the inventory.  Meanwhile,
bike frames will come in different configurations to take advantage of
the special wheel sizes.  SIzes whose advantages are imperceptibly small
but are touted by riders who talk of seconds saved in their last club TT
or while riding to work.

A larger wheel rides better on average roads and always corners better
because it brings a longer contact patch to the road.  A longer contact
averages traction over more pavement and avoids slip outs for lack of
local traction.  Visualize crossing a one inch wide glossy paint stripe
with a 27" wheel and an 18" wheel when banked over in a wet turn.

I see this subject arise now and then and it reminds me of the concept of
splitting wreck.bike into several newsgroups.  The perpetrators bring the
matter up for many of the wrong reasons.

Ride bike, don't re-invent what has been discarded.

------------------------------

Subject: 8c.5   Tied and Soldered Wheels
From:  Jobst Brandt <[e-mail]>
Date: Mon, 16 Dec 1996 15:09:03 PST

While writing "the Bicycle Wheel", to conclusively determine what
effect tying and soldering of spoke crossings in a wheel had, I asked
Wheelsmith to loan me an untied pair of standard 36 spoke rear wheels,
on on Campagnolo low and high flange hubs.  I had an inner body of a
freewheel machined with flats so that a wheel could be clamped into
the vise of a Bridgeport milling machine while the left end of its
axle was held in the quill.

With the hub rigidly secured, with its axle vertical, dial gauges were
mounted at four equally spaced locations on the machine bed to measure
rim deflections as a 35lb weight was sequentially hung on the wheel at
these positions.  The deflections were recorded for each location and
averaged for each wheel before and after tying and soldering spokes.

The wheels were also measured for torsional rigidity in the same
fixture, by a wire anchored in the valve hole and wrapped around the
rim so that a 35 lb force could be applied tangential to the rim.
Dial gauges located at two places 90 degrees apart in the quadrant
away from the applied load were used to measure relative rotation
between the wheel and hub.

Upon repeating the measurements after tying and soldering the spokes,
no perceptible change, other than random measurement noise of a few
thousandths of an inch, was detected.  The spokes were tied and
soldered by Wheelsmith who did this as a regular service.  The data
was collected by an engineer who did not know what I expected to find.
I set up the experiment and delivered the wheels.

------------------------------

Subject: 8c.6  Machined rims
From:  Jobst Brandt <[e-mail]>
Date:    Sun, 26 Jan 2003 19:57:48 -0800 (PST)

> Just wondering if it really makes any difference.  Some
> manufacturers don't even advertise whether the sidewalls are
> machined; others do.  Velocity for example, makes both, but I
> believe they're the same price.  What gives?  Just marketing hype?

What you hear and read is mostly marketing hyperbole, but machining
rims has its reason, and it isn't for your benefit.  If you inspect a
machined rim closely, you'll find a surface that looks as though made
by a thread cutting tool.  The purpose is not to get a flat braking
surface, but rather to produce a series of fine grooves to prevent
brake squeal on new bicycle test rides.

The machined grooves, about the texture of LP vinyl record grooves,
can be felt by running a fingernail across the rim.  These fine
grooves usually wear off on the first braking descent in wet weather,
the condition that causes rim wear in the first place.  Even
anodizing, which is a hard ceramic, whether thick or thin, is more
durable than the machined rim.  However, anodizing is not the solution
to wear, because it degrades braking.  Anodizing being an insulator
that overheats brake pads and causes brake fade.

The claim that machining is for purposes other than suppressing brake
squeal is far fetched.  For instance, rim joints have been made with
no perceptible discontinuity almost as long as aluminum rims have been
made.  Unfortunately, some people in marketing believe that rims will
separate if not riveted (or welded) and introduced riveting that
usually distorts rim joints.  Fortunately, that rims were made for
many years without rivets and had flawless joints proves otherwise.

In practice, machining solves the new-rim squeal problem at the cost
of a rim wall of unknown thickness.  It also adds a bit of sparkle to
the new product by giving rainbow reflections in showrooms.  Mavic,
for instance, has rims listed as having "CERAMIC2", "SUP, "CD", "UB",
MAXTAL", all features that substantially increase cost over plain
aluminum rims that were offered at about 1/4 the price not long ago.

The web site explains that "CERAMIC2" is an insulator that improves
braking even though the rim is "UB" machined, ostensibly for the same
purpose, before ceramic coating.  This is a tipoff, because without
special brake pads, this feature overheats pads causing them to wear
rapidly while degrading performance.  Not mentioned is that it's main
purpose is to reduce rim wear in wet and gritty conditions.

------------------------------

Subject: 8c.7  Wheel Bearing adjustment
From: Jobst Brandt <[e-mail]>
Date:    Sun, 23 Mar 2003 12:21:02 -0800 (PST)

Bicycle wheel bearings, as most, require a slight preload so that more
than one ball under the cone (inner race) will support its load.  With
proper preload, slight drag should be perceptible.  Preload drag is
small compared to drag caused by wheel loads, neither of which are
significant regardless of adjustment. In contrast bearing life is
affected by proper adjustment.  Adjusting ball bearings to spin freely
unloaded does not reduce operating friction because a bearing with
proper preload has lower drag when loaded than one with clearance.
For high quality bearings, preload should be just enough to cause
light drag when rotating the axle between thumb and forefinger.  Low
grade bearings will feel slightly lumpy with proper preload.

Wheels with quick release (QR) axles present an additional problem in
that closing the QR alters bearing clearance.  Closing the lever
requires increasing manual force with a slight over-center feel near
the end of the stroke.  This lever force arises from compressing the
hollow axle and stretching the skewer.  The ratio of elastic length
change between axle and skewer is that of their cross sectional area
and active lengths.

Although small, axle compression on QR hubs is large enough to alter
bearing clearance and should be considered when adjusting bearings.
Bearings should be adjusted just loose enough so that closing the QR
leaves the bearing with a slight preload.  Excessive preload from QR
closure is the cause of most wheel bearing failures not caused by
water intrusion.  Clearance, in contrast can be felt as disconcerting
rattle when encountering road roughness.

To test for proper adjustment, install the wheel and wiggle the rim
side-to-side to determine that there is no clearance (rattle), then
let the wheel rotate freely to a stop.  If the wheel halts with a
short (indexed) oscillation, bearing preload is too high.

Although adjusting QR force is a safety consideration, it is also one
of bearing life.  It should be kept at a constant level once the
desired closure force has been determined.  Rear vertical dropouts
require a lower and more predictable closure force than was formerly
required with axles that could move forward from chain tension.
Because vertical dropouts do not rely on friction to resist chain
load, many hubs now have smooth faced jam nuts that do not damage
dropout faces as older knurl faced ones did.

------------------------------

Subject: 8d  Tech Chains

------------------------------

Subject: 8d.1   Lubricating Chains

Lubricating chains is a somewhat religious issue.  Some advocate oil,
some Teflon-base lubricants, some paraffin wax.  The net majority favors
a lubricant that does not leave an oily coating on the chain that can
attract dirt, which will hasten chain/chainring/freewheel sprocket wear.

If you want to use paraffin wax, make sure you melt the wax in a double
boiler!  Failure to do so can lead to a fire.  You can use a coffee
can in a pan of boiling water if you don't want to mess up good cookware.
After the wax has melted, put the chain in the wax and simmer for 10
minutes or so.  Remove the chain, hang it up, and wipe the excess wax
off.  Let it cool and reinstall on your bike.

When using a liquid lubricant, you want to get the lube onto the pins
inside the rollers on the chains, not on the outside where it does little
good.  Oilers with the narrow tubes are good for this because you can put
the lube where you want it.  Work the oil into the chain after applying
it, wipe the chain off, and reinstall on your bike.

A good discussion of chain maintenance is at

  http://www.sheldonbrown.com/chains.html

------------------------------

Subject: 8d.2   Chain care, wear and skipping
From:  Jobst Brandt <[e-mail]>
Date:    Thu, 10 Jan 2002 17:40:52 -0800 (PST)

Chain wear and care evokes never ending discussions, especially for
new bicyclists who are not happy with this dirtiest of bicycle parts.
This leads to the first problem, of whether there is a best (and
cleanest) way to care for a chain.  There are several ways to take
care of a chain of which some traditional methods are the most
damaging to the chain and others work to prolong its life.

That grease on a new chain, fresh out of the package, is not a
lubricant but rather a preservative that must be removed, thrives in
bicycling myth and lore.  This is nonsense because chains are used as
they are by manufacturers who ship bicycles ready to use.  They can
order chains with any desired lubricant and this is what they use.  If
there is too much on the chain, it can be wiped off.

At the outset the term "chain stretch" is technically wrong and
misleading.  Chains do not stretch, in the dictionary sense, by
elongating the metal through tension.  They lengthen because their
hinge pins and sleeves wear which is caused almost exclusively by road
grit that enters the chain when oiled.  Grit sticks to the outside of
a chain in the ugly black stuff that can get on ones leg, but external
grime has little functional effect, being on the outside where it does
the chain no harm.  Only when a dirty chain is oiled, or has excessive
oil on it, can this grit move inside to causes damage.  Commercial
abrasive grinding paste is made of oil and silicon dioxide (sand) and
silicon carbide (sand).  You couldn't do it better if you tried to
destroy a chain, than to oil it when dirty.

Primitive rule #1: Never oil a chain on the bike.

This means the chain should be cleaned of grit before oiling, and
because this is practically impossible without submerging the chain in
a solvent bath (kerosene or commercial solvent), it must be taken off
the bicycle.  Devices with rotating brushes, that can be clamped on
the chain on the bicycle, do a fair job but are messy and do not
prevent fine grit from becoming suspended in the solvent.  External
brushing or wiping moves grit out of sight, but mainly into the
openings in the chain where subsequent oiling will carry it inside.

Do not use gasoline because it is explosive and contains toxic light
petroleum fractions that penetrate skin.  Removing the chain from the
bicycle isn't always possible.  There are times (after riding in the
rain) when a chain screams for oil and good cleaning is impractical.
In that case rule #1 may be violated for humanitarian reasons.
However, only an internally clean chain squeaks, so it isn't as bad as
it sounds.  Also, water is a moderately good lubricant, but it
evaporates soon after the rain stops.

Removing solvent from the chain after rinsing is important.
Compressed air is not readily available in the household nor is a
centrifuge.  Manually slinging the chain around outdoors works best if
the chain is a closed loop but without pressing the pin completely in.
The other way is to evaporate it.  Accelerated drying methods by
heating should be avoided, because they can be explosive.

Lubricating the chain with hot 90W gear lube works but it is also
efficient fly paper, collecting plenty of hardpack between sprockets
and on the outside of the chain.  Motor oil is far better, but
motorcycle chain and chainsaw lubricants are better yet, because they
have volatile solvents that allow good penetration for their
relatively viscous lubricant.  Paraffin (canning wax), although clean,
works poorly because it is not mobile and cannot replenish the bearing
surfaces once it has been displaced.  This becomes apparent with any
water that gets on the chain.  It immediately squeaks.

Swaged bushing chains

Sedis was the first with its Sedisport (five element) chain to
introduce swaged bushings, formed into the side plates, to replace
(six element) chains with full width steel bushings on which the
rollers and pins bear.  Although stronger and lighter than prior
chains, the five element chain achieves its light weight at the
expense of durability.  These chains, now the only derailleur chains
available, have only vestigial sleeves in the form of short collars on
the side plates to support the roller on the outside and the link pin
on the inside.  This design is both lighter and stronger because the
side plates need not have the large hole for insertion of sleeves.

Pins inside full bushings of (six element) chains were well protected
against lubricant depletion because both ends were covered by closely
fitting side plates.  Some motorcycle chains have O-ring seals at each
end.  In the swaged bushing design there is no continuous tube because
the side plates are formed to support the roller and pin on a collar
with a substantial central gap.  In the wet, lubricant is quickly
washed out of pin and roller and the smaller bearing area of the
swaged bushing for the pin and roller easily gall and bind when
lubrication fails.  Although this is not a problem for this type of
chain when dry it has feet of clay in the wet.

Chain Life

Chain life is almost entirely a cleanliness and lubrication question
rather than a load problem.  For bicycles the effect of load
variations is insignificant compared to the lubricant and grit
effects.  For example, motorcycle primary chains, operated under oil
in clean conditions, last as much as 100,000 miles while exposed rear
chains must be replaced often.

The best way to determine whether a chain is worn is by measuring its
length.  A new chain has a half inch pitch with a pin at exactly every
half inch.  As the pins and sleeves wear, this spacing increases,
concentrating more load on the last tooth of engagement, changing the
tooth profile.  When chain pitch grows over one half percent, it is
time for a new chain.  At one percent, sprocket wear progresses
rapidly because this length change occurs only between pin and sleeve
so that it is concentrated on every second pitch; the pitch of the
inner link containing the rollers remaining constant.  By holding a
ruler along the chain on the bicycle, align an inch mark with a pin
and see how far off the mark the pin is at twelve inches.  An eighth
of an inch (0.125) is one percent, twice the sixteenth limit that is a
prudent time for a new chain.

Skipping Chain

Sprockets do not change pitch when they wear, only their tooth form
changes.  The number of teeth and base circle remain unchanged by
normal sprocket wear.

A new chain often will not freely engage a worn rear sprocket under
load even though it has the same pitch as the chain.  This occurs
because the previous (worn and elongated) chain formed pockets higher
on each tooth (a larger pitch diameter) than an in pitch chain
describes.  This wear occurs because a worn chain rides high on the
teeth.  A chain with correct pitch cannot enter the pockets when its
previous roller bears the previous tooth, because the pocket has an
overhang that prevents entry.

Without a strong chain tensioner or a non derailleur bicycle, the
chain has insufficient force on its slack run to engage a driven
sprocket.  In contrast, engagement of a driving sprocket, the crank
sprocket, generally succeeds even with substantial tooth wear, because
the drive tension forces engagement.

However, worn teeth on a driving sprocket cause "chainsuck", the
failure of the chain to disengage.  This occurs more easily with a
long arm derailleur, common to most MTB's, that is one reason this
occurs less with road racing bicycles, that experience a noisy
disengagement instead.

In contrast a worn chain will not run on a new driving sprocket.  This
is less apparent because new chainwheels are not often used with an
old chain.  In contrast to a driven (rear) sprocket the chain enters
the driving (front) sprocket under tension, where the previous chain
links pull it into engagement.  However, because a used chain has a
longer pitch than the sprocket, previous rollers bear almost no load
and allow the incoming chain link to climb the ramp of the tooth, each
successive link riding higher than the previous until the chain jumps.
The pockets in a used sprocket are small but they change the pressure
angle of the teeth enough to cause skipping.

Jobst Brandt      <[e-mail]>

------------------------------

Subject: 8d.3   Adjusting Chain Length
From: Bob Fishell <[e-mail]>

For all Shimano SIS and Hyperglide systems, the chain is sized by shifting to
the smallest rear cog and the largest front sprocket, then sizing the
chain so that the derailleur pulleys are on a vertical line, or as close
as you can get to it.  Note that this will result in the same chain length
for any freewheel within the capacity of the derailleur, so it usually is
not necessary to re-size the chain for a different cogset with these systems.

The other rule I've used (friction systems) involves shifting to the largest
chainring and the largest rear cog, then sizing the chain so that the pulleys
are at a 45 degree angle to the ground.

The rules probably vary from derailleur to derailleur.  In general,
you may use the capacity of the rear derailleur cage as a guideline. You
want the chain short enough so the cage can take up the slack in the
smallest combination of chainwheel and rear cog you will use. The chain
must also be long enough so that the cage still has some travel in the
largest combination you will use.

For example, if you have a 42x52 crank and a 13x21 freewheel, the smallest
combination you would use would be a 42/14 (assuming you don't use the
diagonal). If the cage can take up the slack in this combo, it's short enough.
If the cage has spring left when you are in the 52/19 combo (again, you are
not using the diagonal), it's long enough.

------------------------------

Subject: 8d.4   Hyperglide chains

For those of you that are tired of dealing with Shimano's
chains with the special pins, I've found that the following
chains work well with Shimano Hyperglide gearing systems:

DID SuperShift
Sedis ATB
Union 800
Union 915

The SuperShift is probably the best performer of the bunch,
followed by the ATB and 915.  The 800 doesn't do too well
with narrow cogsets (i.e., 8-speeds) because the raised
elliptical bumps on the side-plates tend to rub on the adjacent
cogs.

I've also found that these chains work well on SunTour systems.
The 915, however, works better on PowerFlo cogs than it does
on regular (AccuShift) cogs (where it tends to slip when shifting).

------------------------------

Subject: 8d.5   SACHS Power-links
From:  Jobst Brandt <[e-mail]>
Date:    Wed, 12 May 1999 15:38:14 PDT

The SACHS Power-link, can be separated easily alone but not when in a
chain.  The link is designed not to open by axial compression alone,
typically when a new chain is used on worn sprockets, where skipping
over teeth can cause inertial compression by the trailing chain.  To
prevent this occurrence, a recess around the head of the stepped pin
makes more than a half circle, preventing the pin from sliding in its
slot.  That means the side plates of the link must be pressed
together, taking up side clearance, to raise the head of the sliding
pin above this retention.

To open the chain, find the link, make an upside down U-shape of the
chain with the link as the cross bar, the adjacent chain hanging down,
grasp the link diagonally with pliers across the the corners to which
the pins are fixed, not the corners with the keyhole slot.  Pushing
the side plates together assists removal but is not essential, the
diagonal force having a lateral compressive component.

Before using a Power-link, put it together to see why it does not
readily slide from closed to open position.  Road grit makes this even
more difficult.

------------------------------

Subject: 8e  Tech Frames

------------------------------

Subject: 8e.1   Bike pulls to one side
From:  Jobst Brandt <[e-mail]>

For less than million dollar bikes this is easy to fix, whether it corrects
the cause or not.  If a bike veers to one side when ridden no-hands, it
can be corrected by bending the forks to the same side as you must lean
to ride straight.  This is done by bending the fork blades one at a time,
about 3 mm.  If more correction is needed, repeat the exercise.

The problem is usually in the forks although it is possible for frame
misalignment to cause this effect.  The kind of frame alignment error
that causes this is a head and seat tube not in the same plane.  This
is not easily measured other than by sighting or on a plane table.
The trouble with forks is that they are more difficult to measure even
though shops will not admit it.  It takes good fixturing to align a
fork because a short fork blade can escape detection by most
measurement methods.  Meanwhile lateral and in-line corrections may
seem to produce a straight fork that still pulls to one side.
However, the crude guy who uses the method I outlined above will make
the bike ride straight without measurement.  The only problem with
this is that the bike may pull to one side when braking because the
fork really isn't straight but is compensated for lateral balance.

This problem has mystified more bike shops because they did not recognize
the problem.  Sequentially brazing or welding fork blades often causes
unequal length blades and bike shops usually don't question this dimension.
However, in your case I assume the bike once rode straight so something
is crooked

------------------------------

Subject: 8e.2   Frame Stiffness
From: Bob Bundy <[e-mail]>

As many of you rec.bicycles readers are aware, there have been occasional,
sometimes acrimonious, discussions about how some frames are so much
stiffer than others.  Cannondale frames seem to take most of the abuse.
The litany of complaints about some bike frames is long and includes
excessive wheel hop, numb hands, unpleasant ride, broken spokes,
pitted headsets, etc.  I was complaining to a friend of mine about how there
was so much ranting and raving but so little empirical data - to which
he replied, "Why don't you stop complaining and do the measurements
yourself?".  To that, I emitted the fateful words, "Why not, after all,
how hard can it be?".  Following some consultation with Jobst and a few
other friends, I ran the following tests:

The following data were collected by measuring the vertical deflection at
the seat (ST), bottom bracket (BB) and head tube (HT) as a result of
applying 80lb of vertical force.  The relative contributions of the
tires, wheels, fork, and frame (the diamond portion) were measured using
a set of jigs and a dial indicator which was read to the nearest .001
inch.  For some of the measures, I applied pressures from 20 to 270 lbs
to check for any significant nonlinearity.  None was observed.  The same
set of tires (Continentals) and wheels were used for all measurements.
Note that these were measures of in-plane stiffness, which should be
related to ride comfort, and not tortional stiffness which is something
else entirely.

Bikes:

TA - 1987 Trek Aluminum 1200, this model has a Vitus front fork, most
     reviews describe this as being an exceptionally smooth riding bike

SS - 1988 Specialized Sirus, steel CrMo frame, described by one review as
     being stiff, hard riding and responsive

DR - 1987 DeRosa, SP/SL tubing, classic Italian road bike

RM - 1988 Cannondale aluminum frame with a CrMo fork, some reviewers
      could not tolerate the rough ride of this bike


               TA              SS              DR              RM
           ----------      ----------      ----------      ----------
       ST  BB  HT      ST  BB  HT      ST  BB  HS      ST  BB  HT
diamond        1   1   0       2   2   0       2   2   0       1   1   0
fork        3  11  45       3   9  36       4  13  55       3  10  40
wheels      2   2   2       2   2   2       2   2   2       2   2   2
tires      68  52  66      68  52  66      68  52  66      68  52  66
total      74  66 113      75  65 104      76  69 123      74  65 108


What is going on here?  I read the bike mags and this net enough to know
that people have strong impressions about the things that affect ride
comfort.  For example, it is common to hear people talk about rim types
(aero vs. non-aero), spoke size, butting and spoke patterns and how they
affect ride.  Yet the data presented here indicate, just a Jobst predicted,
that any variation in these factors will essentially be undetectable to
the rider.  Similarly, one hears the same kind of talk about frames,
namely, that frame material X gives a better ride than frame material Y, that
butted tubing gives a better ride that non-butted, etc.  (I may have even
made such statements myself at some time.)  Yet, again, the data suggest
that these differences are small and, perhaps, even undetectable.  I offer
two explanations for this variation between the data and subjective reports
of ride quality.

Engineering:
These data are all static measurements and perhaps only applicable at the
end of the frequency spectrum.  Factors such as frequency response, and
damping might be significant factors in rider comfort.

Psychology:
There is no doubt that these bikes all look very different, especially the
Cannondale.  They even sound different while riding over rough
roads.  These factors, along with the impressions of friends and reviews
in bike magazines may lead us to perceive differences where they, in fact,
do not exist.

Being a psychologist, I am naturally inclined toward the psychological
explanation.  I just can't see how the diamond part of the frame contributes
in any significant way to the comfort of a bike.  The damping of the frame
should be irrelevant since it doesn't flex enough that there is any
motion to actually dampen.  That the frame would become flexible at
some important range of the frequency spectrum doesn't seem likely either.

On the other hand, there is plenty of evidence that people are often very
poor judges of their physical environment.  They often see relationships
where they don't exist and mis-attribute other relationships.  For example,
peoples' judgement of ride quality in automobiles is more related to the
sounds inside the automobile than the ride itself.  The only way to get
a good correlation between accelerometers attached to the car seat and
the rider's estimates of ride quality is to blindfold and deafen the
rider (not permanently!).  This is only one of many examples of mis-
attribution.  The role of expectation is even more powerful.  (Some even
claim that whole areas of medicine are built around it - but that is
another story entirely.)   People hear that Cannondales are stiff and,
let's face it, they certainly *look* stiff.  Add to that the fact that
Cannondales sound different while going over rough roads and perhaps
the rider has an auditory confirmation of what is already believed to
be true.

Unless anyone can come up with a better explanation, I will remain
convinced that differences in ride quality among frames are more a
matter of perception than of actual physical differences.

------------------------------

Subject: 8e.3   Frame repair
From: David Keppel <[e-mail]>

(Disclaimer: my opinions do creep in from time to time!)

When frames fail due to manufacturing defects they are usually
replaced under warranty.  When they fail due to accident or abuse
(gee, I don't know *why* it broke when I rode off that last
motorcycle jump, it's never broken when I rode it off it before!)
you are left with a crippled or unridable bike.

There are various kinds of frame damage that can be repaired.  The
major issues are (a) figuring out whether it's repairable (b) who
can do it and (c) whether it's worth doing (sometimes repairs just
aren't worth it).

Kinds of repairs: Bent or cracked frame tubes, failed joints, bent
or missing braze-on brackets, bent derailleur hangars, bent or
broken brake mounts, bent forks, etc.  A frame can also be bent out
of alignment without any visible damage; try sighting from the back
wheel to the front, and if the front wheel hits the ground to one
side of the back wheel's plane (when the front wheel is pointing
straight ahead), then the frame is probably out of alignment.


* Can it be repaired?

Just about any damage to a steel frame can be repaired.  Almost any
damage to an aluminum or carbon fiber frame is impossible to repair.
Titanium frames can be repaired but only by the gods.  Some frames
are composites of steel and other materials (e.g., the Raleigh
Technium).  Sometimes damage to steel parts cannot be repaired
because repairs would affect the non-steel parts.

Owners of non-steel frames can take heart: non-steel frames can
resist some kinds of damage more effectively than steel frames, and
may thus be less likely to be damaged.  Some frames come with e.g.,
replacable derailleur hangers (whether you can *get* a replacement
is a different issue, though).  Also, many non-steel frames have
steel forks and any part of a steel fork can be repaired.

Note: For metal frames, minor dents away from joints can generally
be ignored.  Deep gouges, nicks, and cuts in any frame may lead to
eventual failure.  With steel, the failure is generally gradual.
With aluminum the failure is sometimes sudden.

Summary: if it is steel, yes it can be repaired.  If it isn't steel,
no, it can't be repaired.


* Who can do it?

Bent derailleur hangers can be straightened.  Indexed shifting
systems are far more sensitive to alignment than non-indexed.  Clamp
an adjustable wrench over the bent hanger and yield the hanger
gently.  Leave the wheel bolted in place so that the derailleur hanger
is bent and not the back of the dropout.  Go slowly and try not to
overshoot.  The goal is to have the face of the hanger in-plane with
the bike's plane of symmetry.

Just about any other repair requires the help of a shop that builds
frames since few other shops invest in frame tools.  If you can find
a shop that's been around for a while, though, they may also have
some frame tools.


* Is it worth it?

The price of the repair should be balanced with

 * The value of the bicycle
 * What happens if you don't do anything about the damage
 * What would a new bike cost
 * What would a new frame cost
 * What would a used bike cost
 * What would a used frame cost
 * What is the personal attachment

If you are sentimentally attached to a frame, then almost any repair
is worth it.  If you are not particularly attached to the frame,
then you should evaluate the condition of the components on the rest
of the bicycle.  It may be cheaper to purchase a new or used frame
or even purchase a whole used bike and select the best components
from each.  For example, my most recent reconstruction looked like:

 * Bike's estimated value: $300
 * Do nothing about damage: unridable
 * Cost of new bike: $400
 * Cost of new frame: $250+
 * Cost of used bike: $200+
 * Cost of used frame: N/A
 * Cost of repair: $100+
 * Personal attachment: zip

Getting the bike on the road again was not a big deal: I have lots
of other bikes, but I *wanted* to have a commuter bike.  Since I
didn't *need* it, though, I could afford to wait a long time for
repairs.  The cost of a new bike was more than I cared to spend.
It is hard to get a replacement frame for a low-cost bicycle.  I
did a good bit of shopping around and the lowest-cost new frame
that I could find was $250, save a low-quality frame in the
bargain basement that I didn't want.  Used frames were basically the
same story: people generally only sell frames when they are
high-quality frames.  Because the bike was a road bike, I could have
purchased a used bike fairly cheaply; had the bike been a fat-tire
bike, it would have been difficult to find a replacement.  The cost
of the frame repair included only a quick ``rattlecan'' spray, so
the result was aesthetically unappealing and also more fragile.  For
a commuter bike, though, aesthetics are secondary, so I went with
repair.

There is also a risk that the `fixed' frame will be damaged.  I had
a frame crack when it was straightened.  I could have had the tube
replaced, but at much greater expense.  The shop had made a point
that the frame was damaged enough that it might crack during repair
and charged me 1/2.  I was able to have the crack repaired and I
still ride the bike, but could have been left both out the money
and without a ridable frame.


* Summary

Damaged steel frames can always be repaired, but if the damage is
severe, be sure to check your other options.  If the bicycle isn't
steel, then it probably can't be repaired.

------------------------------

Subject: 8e.4   Frame Fatigue
From: John Unger <[e-mail]>

I think that some of the confusion (and heat...) on this subject
arises because people misunderstand the term fatigue and equate it
with some sort of "work hardening" phenomena.

By definition, metal fatigue and subsequent fatique failure are
well-studied phenomena that occur when metal (steel, aluminum,
etc.) is subjected to repeated stresses within the _elastic_ range
of its deformation. Elastic deformation is defined as deformation
that results in no permanent change in shape after the stess is
removed. Example: your forks "flexing" as the bike rolls over a
cobblestone street.

    (an aside... The big difference between steel and aluminum
    as a material for bicycles or anything similar is that you
    can design the tubes in a steel frame so that they will
    NEVER fail in fatigue. On the other hand, no matter how
    over-designed an aluminum frame is, it always has some
    threshold in fatigue cycles beyond which it will fail.)

This constant flexing of a steel frame that occurs within the
elastic range of deformation must not be confused with the
permanent deformation that happens when the steel is stressed beyond
its elastic limit, (e. g., a bent fork). Repeated permanent
deformation to steel or to any other metal changes its strength
characteristics markedly (try the old "bend a paper clip back and
forth until it breaks" trick).

Because non-destructive bicycle riding almost always limits the
stresses on a frame to the elastic range of deformation, you don't
have to worry about a steel frame "wearing out" over time.

I'm sorry if all of this is old stuff to the majority of this
newsgroup's readers; I just joined a few months ago.

I can understand why Jobst might be weary about discussing this
subject; I can remember talking about it on rides with him 20 years
ago....

------------------------------

Subject: 8e.5   Frames "going soft"
From: [e-mail] (Jobst Brandt)
Date:    Mon, 20 Apr 1998 15:31:32 PDT

> I have read accounts of "frames going dead" in cycling literature in
> the past.  If you have information that debunks this, I'd like to
> know about it.  The explanations I have read claim that the flexing
> of a metal causes it to heat up and harden, making it more brittle.
> Eventually it will break under stress.  In fact, I read recently
> that aluminum frames are coming out with warning stickers stating
> "this frame will break someday".  I have also read that this happens
> to titanium and steel.

It was in print, therefore it is true!  Also known, is that a freshly
washed and polished car runs better.  Just the idea that the car is
admirably clean makes this concept appear true for many drivers.  The
same psychosomatic mechanism is at work when a bicycle racer thinks it
is time for a new frame.  I even suspect that some frame builders
assisted in spreading this idea to improve frame sales.

Metal fatigue and failure occur, but they do not change the elastic
response of the metal.  Steel (and of course aluminum and other common
metals) have been metallurgically characterized over more than a
century to a precise understanding.  None of this research has shown
the possibility of perceptible change in elastic response from any
stresses to which a bicycle frame might be subjected.

You mention brittleness.  Brittleness describes the failure mode of a
material and is not a perceptible unless the material breaks.
Hardness is also not perceptible unless you exceed the elastic limit
and permanently bend the frame, exposing the metal's yield point, the
point at which it no longer rebounds.  If not, it springs back
unchanged as do most ceramics such as a dish, or a glass that is
dropped without breaking.  If it breaks, it does not bend and none of
the shards show any distortion.  It either breaks or it doesn't.
That's brittleness personified.

What escapes the believers of material change is that neither
"softening" or "hardening" effects the elastic modulus of the metal.
A coat hanger and a highspeed steel drill of the same diameter have
the same elastic bending stiffness.  For small bending deflections,
both are equally stiff, although the hardened steel can bend farther
than the soft steel and still spring back unchanged.  The stress at
which it permanently deforms is the measure of "hardness" of the
metal, not its elasticity.

Classically, when bicycle parts or frames fail, the rider usually
notices nothing before hand.  This is true for most thick cross
section parts and often even frame tubes frames.  The reason for this,
is that to permit any perceptible change in deflection, all the added
elasticity must come from a crack that has practically no volume.  So
the crack would need to open substantially to, by itself, allow
perceptible motion.  Since this is not possible without complete
failure, the crack grows in length, but not width, until the remaining
cross section can no longer support the load, at which time it
separates.

> If these ideas have been widely disproven, I'd appreciate knowing
> how.  I've read all six parts of the FAQ and did not see it mentioned.

The reason this was not in the FAQ may be that the whole subject is so
preposterous to engineers, metallurgists, and physicists, that they,
the people who might explain it, are generally not inclined to bother
discussing whether "the moon is made of green cheese" or not.

> PS. If what you're objecting to is the use of the word "dead" as
> opposed to brittle and inflexible, I'll grant you that.

The objection is that you present something for which there is no iota
of scientific evidence, nor any even slightly credible explanation, as
though it were fact.  It is as though bicyclists have a different
natural world, where the technical laws are entirely different from
all other machinery, and the most perceptive technical insights come
from the strongest bicycle racers.  "After all who knows more about
bicycles, you or the world champion?" is a common retort.

Jobst Brandt      <[e-mail]>

------------------------------

Subject: 8e.6   Inspecting your bike for potential failures
From: [e-mail] (Keith Bontrager)

Handlebars are probably the one component that deserves the most
respect.  Easton recommends a new bar every two years.  I don;t recall
if they include an "if you race" preface.  I'd say that's probably
about right.  Same for our aluminum bars.  Yearly would be good
on bars that have not been engineered for extended fatigue lives.

Of course, if you don;t race, if you have more than one bike, if
you are a smooth rider, if you like to do "skyshots" you need to
work this in to the estimate.  Getting tougher, eh?  Many people
could ride on the good quality bars into the next millenium without
a problem.  How do you sort it out?  I don't know.

Many parts (not bars or forks) will give you ample warning if you bother
to inspect your bike regularly.  Clean it.  Look at it.  There
are "hot spots" all over the bike that deserve carefull attention.

Fork crown.  Welds if a rigid fork, crown material if its a sus fork.

Steerer.  Hard to look at, but once a year, especially if it's aluminum
or if you've crashed hard with a big front impact.  Also if there are
noises from the front of the bike when you climb or sprint, or
if the bike starts handling funny.  Be careful when you change lower
head set races so you don't gouge up the steerer at the bottom.

If you have an AHS stem/steerer look at the steerer at the point
where the stem and HS bearings meet.  Critical!

Stem.  All of the welds and the binder.  Especially if you are
a 200lb sprint specialist.

Down tube/head tube joint of the frame - underneath.

Top tube/ head tube joint - same location.

Seat tube - near the BB shell and near the seat binder clamp slot.

BB spindle.  Hard to look at, but once a year.  Look near the tapers
where the crank fits on.  This is the weak spot.  If the crank
feels funny when you are pedaling (hard to describe the feeling)
or if it comes loose unexpectedly, look long and hard at the spindle.
Cartridge BBs that allow you to change the bearings should be
treated with some respect.  You can keep fresh bearings in them
forever, guaranteeing that they'll be in service until the
spindle fails!

Cranks.  Check the right hand arm all around where the arm leaves
the spider.  Also check the hub where the arm attaches to the
spindle - especially if the arm is machined from bar (CNC).  The
section near the pedal threads was prone to failure on older
road cranks though I have not seen this on MTB cranks (yet!).
Look all over the arms on the light aftermarket cranks.  Often.
Twice.

Seat post.  Pull it out and sight down the quill.  Any ripples
or deformation around the area where the post is clamped in the
frame indicates a failure on the way.  The clamps are too varied to
comment on.  If you have to run the fasteners real tight to keep
the saddle from slipping you should put new, very high strength
fasteners in every year or so.  The clamps can come loose from the
quill tube sometimes (ask me how I know).  Grab the saddle and give it
a twist.

Saddle.  Rails near the seat post support pieces.

Rims.  material around spoke holes can pull out, side walls can
wear through, side walls can fail due to extrusion defects.  Some
of these are hard to see.

Frames around the dropouts (not a problem with newer frames as it
was with older campy forged drops).  Chainstays near the CS bridge
and BB shell.

Hubs.  Flanges can pull away from the hub body.  Not a problem
in most cases unless the wheels are poorly built, you are running
radial spokes and ride real hard, have poorly designed aftermarket
hubs, or are very unlucky.

Many components will make a bit of noise or make the bike feel funny
before they go.  Not all will.  Respect this.

------------------------------

Subject: 8e.7   Frame materials
From:    Sheldon Brown <[e-mail]>
Date:    Mon, 27 Nov 2000 04:10:19 GMT

See http://sheldonbrown.com/frame-materials.html

------------------------------

Subject: 8e.8  Bottom Bracket Drop
From:  Jobst Brandt <[e-mail]>
Date:    Mon, 10 Jul 2000 16:09:46 PDT

I'm not familiar with BB drop.  How is it measured and what are its
limits?

For road bicycles, using conventional sized wheels, BB drop (BB
spindle centerline below wheel axle centerlines) has been empirically
arrived upon at about [240mm minus crank length] for useful cornering
clearance.  Imbalance of pedaling in curves at greater lean causes
side-slip.  For this reason, higher BB's have shown no advantage in
criterium racing while road races are practically unaffected by
maximum cornering ability while pedaling.  Track bicycles have certain
advantages on tracks with low banking if they can ride the curves at
zero speed but then that depends on track length and how it is banked.

------------------------------

Subject: 8e.9  Bent Frames
From:  Jobst Brandt <[e-mail]>
Date:    Wed, 03 Jan 2001 16:50:20 PST

How to determine whether a frame is straight after a crash and what
can be done about it.

First is visual, especially for head-on collisions on a standard steel
frame, on which top and down tubes generally bend at the end of their
butted section, about 50-100mm from the head tube.  This usually
causes cracks in the paint and can be detected by laying a straight
edge on the down tube.  Next, sight down the fork to determine if the
fork blades are straight in the fore and aft plane, and whether their
upper straight portion is parallel to head tube.  Bicycles with
straight blade forks (with angled crown) make the latter impossible.

Another simple test is to ride no-hands and see whether the bicycle
rides straight.  This will show whether the fork is laterally correct.

Determining whether the "rear triangle" is displaced requires
measurement.  The rear triangle, actually a tetrahedron (four sided
figure with six edges), is not easily bent except by side force on the
BB.  Tubes bent by a force at midspan are self evident by no longer
being straight.  Bicycles with curved stays are on their own here,
having no credible reason for their curvature, which becomes apparent
when trying to determine whether they are "straight."

Rear triangle displacement is measured by stretching a string from one
dropout over the head tube back to the same place on the opposite
dropout.  The distance between string and seat tube should be
identical for both sides.  Also, because the two sides of a frame are
seldom identically strong, dropout spacing will most likely not be
correct, one side having yielded differently than the other.

Such lateral displacements can be manually corrected by laying the
frame on its side, placing the foot on the inside of the lower
chainstay at the BB and pulling the dropout of the upper side toward
the correct position.  Monitor position change by measuring dropout
spacing.  After advancing a few millimeters, put the foot on top of
the upper chainstay at the BB and pull the lower dropout until the
spacing is correct and repeat the sting measurement.

Laterally correcting a front fork is done similarly while monitoring
dropout spacing.  Here the critical test is whether the bicycle rides
no-hands straight, which is relatively easy considering that the only
the wheel need be removed to perform the bend.  Otherwise, sighting
down the head tube onto a dummy axle with a centerline on it can help
determine whether the fork is "on axis."  Forks are best straightened
with fixturing but can be done without.

For steel frames, these operations pose no problem if the distortion
is within limits that do not peel off paint.  Frames with oversized
tubes generally make their fatal bends self evident by wrinkling as do
downtubes of standard steel frames in head-on collisions.

------------------------------

Subject: 8e.10  Aligning a Fork
From:  Jobst Brandt <[e-mail]>
Date: Fri, 11 May 2001 16:35:42 PDT

aka Bicycle pulls to one side

Riders occasionally complain that their bicycle pulls to one side when
ridden no-hands.  That is, the rider must lean off to one side to ride
straight ahead.  This symptom can be from a wheel that is in crocked,
something that is easily checked by observing whether the tire is
centered under the brake bolt, or by just reversing the wheel to see
if the wheel is improperly centered.

Assuming the bicycle still pulls to one side, the reason is usually
that the fork is bent from a side impact.  Bent from a frontal impact
this is easily seen because the blades have a rearward bend just below
the fork crown where the blades should be straight both fore and aft
and side to side.  A frontal bend usually gives a side bend because
the blades are not identical and tend to skew to one side.  This is
harder to fix and requires fixturing.

If the fork is only bent to the side, the correction must be to the
side to which the rider must lean when riding no-hands.  This bend can
be done carefully by bending one blade at a time.

Lay the bicycle on its side, front wheel removed.  Place the rubber
soled foot inside the crown of the fork and pull the upper blade until
the gap at the fork end increases by a couple of millimeters.  This
should be measured.  With the foot in the same place pull the other
fork blade until the original spacing is restored.  Ride the bicycle
and assess the difference.  Repeat if necessary.  This must be done
with a strong arm and a bit of skill but it is simple.

If you have a non steel bicycle, buy a new fork.

------------------------------

Subject: 8e.11  Stuck Handlebar Stem
From:  Jobst Brandt <[e-mail]>
Date: Fri, 11 May 2001 16:35:42 PDT

Frozen aluminum stems were a common occurrence because conventional
stems were poorly anchored in the fork, having only an expander at the
bottom and the top free to pump from side to side with handlebar
forces.  This was OK in the days of steel stems and steel steer tubes
but aluminum accelerated corrosion in this interface, expanding
greatly with oxidation,  in spite of grease in the interface that
only turns to an emulsion in the rain from lateral pumping action.

The expander bolt must be backed off about 1/2 inch to hammer the
expander wedge out of engagement with the bottom of the stem.  When
the expander is free, the bolt should be loose with the expander
dangling on its other end down in the steer tube.  Now the stem should
be rotatable with moderate force.  If this is not the case, then it is
a corroded frozen stem.  Many forks have been damaged by twisting the
bars forcefully in an attempt to free the stem.  Don't do it.  Pouring
ammonia onto the gap is ineffective unless the stem is not truly
frozen.  The thin oxide interface to be dissolved is thousands of
times as deep as thick.  There being no circulation, this method works
only in abstract theory.

A skilled mechanic can saw off and drill the stem out until it is a
thin shell, then break through one side of the shell with a grinder to
extract the stem.  Because aluminum corrosion expands enough to
stretch the steel steer tube, it cannot be loosened by force.  Riders
often are happy when their stem stops creaking only to find later why
it got quiet.  It was no longer removable.  The main advance achieved
by threadless head bearings is that the stem is no longer subject to
this failure.  It is more a stem improvement than a head bearing
improvement, although it also makes adjustment simpler and less
expensive.

Get it removed by a competent shop.  Frame builders do this regularly.

------------------------------

Subject: 8f  Tech Moving Parts

------------------------------

Subject: 8f.1   SIS Adjustment Procedure
From: Bob Fishell <[e-mail]>

Shimano's instructions for adjusting SIS drivetrains varies from series
to series.  The following method, however, works for each of mine (600EX,
105, and Deore').  [Ed note:  Works on Exage road and mtb also.]

Your chain and cogs must be in good shape, and the cable must be free
of kinks, slips,  and binds.  The outer cable should have a liner.
clean and lubricate all points where the cable contacts anything.

SIS adjustment:

1) Shift the chain onto the largest chainwheel and the smallest cog,
   e.g., 52 and 13.

2) WITHOUT TURNING THE CRANKS, move the shift lever back until it
   clicks, and LET GO.  This is the trick to adjusting SIS.

3) Turn the crank.  If the chain does not move crisply onto the next
   inside cog, shift it back where you started, turn the SIS barrel
   adjuster (on the back of the rear derailleur) one-half turn CCW,
   and go back to step 2.  Repeat for each pair of cogs in turn
   until you can downshift through the entire range of the large
   chainwheel gears without the chain hesitating.  If you have just
   installed or reinstalled a shift cable, you may need to do this
   several times.

4) Move the chain to the small chainring (middle on a triple) and the
   largest cog.

5) turn the cranks and upshift.  If the chain does not move crisply
   from the first to the second cog, turn the SIS barrel adjuster
   one-quarter turn CW.

If the drivetrain cannot be tuned to noiseless and trouble-free
SIS operation by this method, you may have worn cogs, worn chain,
or a worn, damaged, or obstructed shift cable.  Replace as needed
and repeat the adjustment.

------------------------------

Subject: 8f.2   SIS Cable Info
From:  Jobst Brandt <[e-mail]>

After Joe Gorin described the SIS "non-compressive" cable housing to
me I got myself a sample to understand what the difference is.  I
believe "non-compressive" is a misnomer.  This cable housing is NOT
non-compressive but rather a constant length housing.  As far as I can
determine, and from reports from bike shops, this housing should not
be used for brakes because it is relatively weak in compression, the
principal stress for brake housing.

SIS housing is made of 18 strands of 0.5mm diameter round spring steel
wire wrapped in a 100mm period helix around a 2.5mm plastic tube.  The
assembly is held together by a 5mm OD plastic housing to make a
relatively stiff cable housing.  Because the structural wires lie in a
helix, the housing length remains constant when bent in a curve.  Each
strand of the housing lies both on the inside and outside of the curve
so on the average the wire path length remains constant, as does the
housing centerline where the control cable resides.  Hence, no length
change.  A brake cable housing, in contrast, changes length with
curvature because only the inside of the curve remains at constant
length while the outside (and centerline) expands.

Shimano recommends this cable only for shift control but makes no
special effort to warn against the danger of its use for brakes.  It
should not be used for anything other than shift cables because SIS
housing cannot safely withstand compression.  Its wires stand on end
and have no compressive strength without the stiff plastic housing
that holds them together.  They aren't even curved wires, so they
splay out when the outer shield is removed.  Under continuous high
load of braking, the plastic outer housing can burst leaving no
support.  Besides, in its current design it is only half as flexible
as brake cable because its outer shell is made of structurally stiff
plastic unlike the brake cable housing that uses a soft vinyl coating.

Because brake cables transmit force rather than position, SIS cable,
even if safe, would have no benefit.  In contrast, with handlebar
controls to give precise shift positioning, SIS housing can offer some
advantage since the cable must move though steering angles.  SIS
housing has no benefit for downtube attached shifters because the
cable bends do not change.

------------------------------

Subject: 8f.3   STI/Ergo Summary
From: Ron Larson <[e-mail]>

This is the second posting of the summary of STI/Ergo experience. The
summary was modified to include more on STI durability and also the
range of shifting avaliable from each system. As before, I am open to
any comments or inputs.

lars

THE CASE FOR COMBINED SHIFTERS AND BRAKES.

Shifters that are easily accessible from either the brakehoods or the
"drop" position are an advantage when sprinting or climbing because the
rider is not forced to commit to a single gear or loose power / cadence
by sitting down to reach the downtube shifters. They also make it much
easier to respond to an unexpected attack.

At first the tendency is to shift more than is necessary. This tendency
levels out with experience. There is also an early tendency to do most
shifting from the bakehoods and the actuators seem to be difficult to
reach from the drop position. This discomfort goes away after a few
hundred miles of use (hey, how many times have I reached for the
downtube on my MTB or thumbshifters on my road bike???).  All
experienced riders expressed pleasure with the ability to shift while
the hands were in any position, at a moments notice.

The disadvantages are extra weight, added weight on the handlebars
(feels strange at first) and expense. Lack of a friction mode was
listed as a disadvantage by a rider who had tried out STI on someone
elses bike but does not have Ergo or STI. It was not noted as a problem
by riders with extended Ergo / STI experience. A comparison of the
weight of Record/Ergo components and the weight of the Record
components they would replace reveals that the total weight difference
is in the 2 to 4 ounce range (quite a spread - I came up with 2 oz from
various catalogs, Colorado Cyclist operator quoted 4 oz of the top of
his head). The weight difference for STI seems to be in the same
range.  The change probably seems to be more because weight is shifted
from the downtube to the handlebars.

There was some concern from riders who had not used either system
regarding the placement of the actuating buttons and levers for Ergo
and STI and their affect on hand positions. Riders with experience have
not had a problem with the placement of the actuators although one
rider stated that the STI brakehoods are more comfortable.

ADVANTAGES OF EACH SYSTEM.

The Sachs/Ergo system was mentioned as a separate system. In fact
(according to publications) it is manufactured By Campagnolo for Sachs
and is identical to the Campagnolo system with the exception of spacing
of the cogs on the freewheel/cassette.  With the Ergo system, all
cables can be routed under the handlebar tape while the STI system does
not route the derailleur cables  under the tape. Those that voiced a
preference liked the clean look of the Ergo system.

Both Ergo and STI seem to be fairly durable when crashed.  Experience
of riders who have crashed with either system is that the housings may
be scratch and ground down but the system still works. The internal
mechanismsof both systems are well protected in a crash.

Both Ergo and STI allow a downshift of about 3 cogs at a time. This
capability is very handy for shifting to lower gears in a corner to be
ready to attack as you come out of the corner or when caught by
surprise at a stop light. Ergo also allows a full upshift from the
largest to the smallest cog in a single motion while STI requires an
upshift of one cog at a time.

Riders voiced their satisfaction with both systems. While some would
push one system over the other, these opinions were equally split.

------------------------------

Subject: 8f.4   Cassette or Freewheel Hubs
From:  Jobst Brandt <[e-mail]>

All cassette hubs are not nearly alike.  That is apparent from the
outside by their appearance and by the sprockets that fit on them.
More important to their longevity is how their insides are designed.
Among the mainline brands, some are a response not only to the choice
and interchangeability of sprockets but to the problem of broken rear
axles and right rear dropouts.  These failures are caused by bending
loads at the middle of the rear axle that arise from bearing support
that is not at the ends of the axle.  The following diagrams attempt
to categorize the freewheel and hub combination, and two cassette
designs with respect to these loads.

                           |
          H             H  | |
          H             H Io-- |
      /-------------------\   -o\
      O                   O------
   ===X==================wX=========    Axle has weak spot at "w"
      O                   O------           (Freewheel & hub)
      \-------------------/   -o/
          H             H Io-- |
          H             H  | |
                           |


                           |
          H             H  | |
          H             H  | | |
      /------------------\ /----\
      O                  O O----O
   ===X==================XwX====X===    Axle has weak spot at "w"
      O                  O O----O         (Hugi and Campagnolo)
      \------------------/ \----/
          H             H  | | |
          H             H  | |
                           |


                           |
          H             H  | |
          H             H  | | |
      /------------------\/o---o\
      O                   \-----O
   ===X=========================X===    Axle is loaded only at ends
      O                   /-----O          (Shimano and SunTour)
      \------------------/\o---o/
          H             H  | | |
          H             H  | |
                           |

For clarity only three sprocket gear clusters are shown.

Strong cyclists put the greatest load on the axle by the pull of the
chain because there is a 2:1 or greater lever ratio from pedal to
chainwheel.  The freewheel in the first diagram has the greatest
overhung load when in the rightmost sprocket.  The second design has
the greatest bending moment on the axle when in the leftmost sprocket
and the third design is independent (in the first order) of chain
position.  This third design carries its loads on bearings at the ends
of the axle for minimum axle stress while the other two put a large
bending moment on the middle of the axle.

Common freewheel hubs have not only the highest bending stress but the
smallest axle at 10mm diameter with threads that help initiate
cracking.  The second design type generally uses a larger diameter
axle to avoid failure.  However, these axles still have significant
flex that can adversely affect the dropout.

There are other important considerations in selecting a hub.
Among these are:

1.  Durability of the escapement and its angular backlash (t/rev).
2.  Flange spacing, offset, and diameter.
3.  Type of bearings (cone / cartridge) and environmental immunity.
4.  Ease of sprocket replacement and cost.

Currently the best solution for sprocket retention is a splined body
that allows individual sprockets to be slipped on and be secured by an
independent retainer.  Screwing sprockets onto the body is
indefensible, considering the difficulty of removal.  The same goes
for freewheels.  No longer needing to unscrew tight freewheels is
another advantage for cassette hubs.

------------------------------

Subject: 8f.5   Cassette or Freewheel Hubs take 2
From: David Keppel <[e-mail]>

People often ask ``should I use a freewheel or a freehub?''  The
answer is usually ``yes.''

The hub is the center of a wheel and is composed of an axle, bolted to
the bike frame, a hub shell or hub body, where the spokes attatch, and
bearings to let the shell rotate around the axle.

Freewheels screw onto threads on the rear hub's shell, and cogs
attatch to the freewheel.  The freewheel's job is to provide a ratchet
between the cogs and the hub shell, so that you can coast.  Freehubs
are similar but combine parts of the freewheel with parts of the hub
shell.  Freehubs are also sometimes called ``cassettes''.

The usual problem with rear hubs is that axles bend and break.  This
is because the axle diameter was chosen when single cogs were used and
the hub bearing was positioned close to the frame.  Since then, wider
cog clusters have become the norm, the bearings and frame have moved
further apart and leverage on the axle has increased.  But since the
axle has not gotten any stronger, it now has a tendency to fail.

Cassettes fix the problem by incorporating one hub bearing in to the
freewheel mechanism, so that the bearing is once again outboard and
the axle is carrying its load under less leverage.  Some freewheel hubs
solve the problem by using fatter axles.  Since increasing the axle
diameter dramatically improves axle strength, this is an effective
solution and it is possible to use a fat axle that is aluminum and thus
lighter than a standard skinny (weaker) steel axle.

Neither solution is perfect -- cassette hubs let you use standard
replacement axles, cones, washers, etc., but force you to use cogs and
spacers and whatnot by a particular manufacturer (and possibly
derailleurs and shifters -- e.g. XTR uses 4.9mm cog-to-cog spacing
instead of the normal 5.0mm).  On the other hand, fat axles are
nonstandard as are some other replacement parts.

As an aside, the cassette solution leaves a fairly long unsupported
axle stub on the left side, and this is sometimes a source of more
bending problems.  Fatter axles solve the problem on both sides.

Note also that many cassette systems allow you to remove the cogs using
a lightweight tool and thus give you ready access to the spokes in case
of breakage.  Freewheels attatch with a fine thread (another historical
artifact, I believe) and are thus more difficult to remove on the road,
making spoke replacement harder.

In principle, freehubs have all cogs attatch using the same size and
shape of spline, so, e.g., a 20T cog can be used as both a large cog
for a corncob cluster and as a middle cog for wide-range cluster.
However, Shimano's marketing is just the opposite and is directed at
selling whole clusters, without letting you replace individual cogs.
(Shimano's policy is relevant here since they sell 90+% of such hubs.)
Freewheels have several spline diameters in order to clear the bearings
and ratchet.  Further, small cogs typically screw on to the freewheel
body or special cogs with extra threads.  This introduces stocking
problems and may make it hard to build some cog combinations.

I'm not a fan of freehubs for the simple reason that they lock me in
to one maker's choices about cogs and cog spacing.  For example, I had
a 1988 Shimano 6-speed freehub and by 1991 Shimano had, according to my
local bike store, discontinued 6-speed replacement cogs.  Thus, simply
replacing one worn cog meant upgrading to a 7-speed system, which in
turn requires all new cogs, a new freehub body (lucky me -- for some it
requires a new hub and thus new wheel), and, if I wanted to keep index
shifting, new thumbshifters.  Had this been a freewheel-equipped
bicycle, I could have easily switched to another maker's 6-speed
freewheels.

Fortunately, the market is stablizing, with a growing number of makers
producing hubs and cogs using a spline pattern like the more recent
Shimano 7-speed freehubs.  However, it hasn't settled entirely, yet.

        ;-D oN  ( A hubalaboo )  Pardo