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Software Vault: The Gold Collection
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Software Vault - The Gold Collection (American Databankers) (1993).ISO
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cdr09
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gearing.zip
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GEAR.DOC
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1993-04-01
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GEAR - A program for optimizing bicycle gearing.
The primary function of the GEAR program is to calculate all of the possible
gear ratios that you can get given the number of teeth on the front and rear
gears of your bicycle. The results are expressed in terms of "equivalent wheel
diameter".
If you have read about the history of bicycles you will remember the great high
wheeled bikes of 1890's that had the pedals attached directly to the front
wheel. Since bicycles of those days lacked gears, the only way you could go
faster was to pedal a bigger wheel.
When geared bicycles were introduced it became possible to get the same effect
by turning a smaller wheel more than one turn for each rotation of the pedals.
The "equivalent wheel diameter" is thus the actual wheel diameter multiplied by
the number of wheel revolutions that occur for each full turn of the pedals.
The GEAR program works a lot like a mini-spreadsheet: there are blanks (or
"cells") on the screen where you fill in values for things like wheel diameter
and the number of teeth on a front or rear gear sprocket.
At the bottom of the screen there is a pseudo graphic display of the equivalent
wheel diameters for all of the possible combinations of gears that you have
entered.
As you enter or change the data, the display at the bottom is updated each time
you type the <Return> (or <Enter>) key. In addition to the graphic display, GEAR
also calculates a more comprehensive numeric display of the gear ratios. This
table is displayed when you press either the <PgUp> or <PgDn> key on the cursor
pad.
The table lists the front and rear sprocket number, the number of teeth on each,
the equivalent wheel diameter, the percentage change from the gear listed above,
the speed obtained in this gear for the specified cadence, and finally the
gradient hill that can be climbed at this speed given the horsepower and weight
of the cyclist.
The GEAR program consists of three essential files:
GEAR.EXE is the main executable file.
GEAR.TPL is the screen template which can be customized.
GEAR.DAT is the data file containing default values.
Once loaded the program will display an introducion and then a short screen of
instructions. Type any key to go on to the next screen. After the initial help
screen you will arrive at the main data entry screen. The data entry screen
looks something like this:
-----------------------------------------------------------------------------
Gear: A program for optimizing bicycle gearing.
Gear Optimization for ________________________________________
Wheel Size ____ (inches) Cadence ___ (rpm)
Weight ___ (lbs) Power ____ (HP) Drag ____ E-5
Front 1 2 3 4 Rear 1 2 3 4 5 6 7
Gear __ __ __ __ Gear __ __ __ __ __ __ __
Percent ____ ____ ____ ____ ____ ____ ____ ____ ____
Rear Front
5 . . . . 1 . . . . . . . . . .
4 . . . . . . 1. . . . . . . . .
3 . . . . . . . . 1 . . . . . .
2 . . . . . . . . . . . 1 . . . .
1 . . . . . . . . . . . . . . 1
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Equivalent Wheel Diameter (inches)
-------------------------------------------------------------------------------
At this point the GEAR program is running much like a specialized spread-sheet
program. The underlined blanks above show up on the screen in reverse video.
These are the blanks or empty cells where you enter the data you want to use.
The cursor pad arrow keys are used to move around the form, and then new values
are entered in any cell location to modify the parameters and gears used in the
calculations.
The graphic display at the bottom of the screen and the percentage difference
between gears are updated when you type <Enter>. In this display each line
corresponds to a gear position on the freewheel and the numbers plotted give the
equivalent wheel diameter for each corresponding chainwheel position.
Moving around the screen:
Keyboard: Action:
Arrow keys: Move left/right char or up/down line.
Ctrl <- and Ctrl -> Move to previous or next field.
<Home> or <End> Move to beginning or end of current line.
<Ins> Toggle between [Insert] and [Overstrike] modes.
<Enter> Update display, filling in blanks if necessary.
<Tab> or Shft<Tab> Update display while changing field.
Ctrl<Home> Clear current entry.
Ctrl<End> Clear entry from cursor to end of field.
Ctrl<PgUp> or <PgDn> Clear all Front or Rear sprocket entries.
PgUp or PgDn Display detailed gear ratio table.
F1 Display this help screen.
F3 Read in pre-set data from disk (Advanced version.)
F9 Print the current table on printer.
The following general information can be entered at the top of the page:
Label: This is just a place where you can enter some text which might
serve as a reminder on a printed copy later on. Put in anything you
want here as a label.
Wheel size: This is where you enter the bicycle's wheel diameter in
inches. It will be used for calculating the effective wheel diameter
for each gear ratio, as well as for speed calculations. According to
the Cateye cyclometer manual, the following values should be used
for metric 700 series wheels:
700 x 23C 26.3"
700 x 25C 26.4"
700 x 28C 26.8"
700 x 32C 27.0"
Cadence: Enter how fast you typically pedal, in rpm. If you don't know,
a good guess would be around 80.
Weight: In this case we want to enter the combined weight of the rider
plus the bicycle. If you don't know what your bike weighs, it is
probably around 30 pounds. If it weighs less than that you probably
paid extra for that weight savings and you know exactly what it
weighs.
HP: Here is where the ego gets involved: you get to estimate how much power you
can put out on a steady basis. If your a recreational cyclist and honest,
you should be in the range 0.1 to 0.3 HP. If you race and don't come in
last, maybe 0.4. If you regularly compete in the Tour de France, I might
give you 0.5 HP. For Albuquerque cyclists, a power output of 0.25 HP will
lift 190 pounds from the Sandia Crest turnoff on North 14 to the top of
Sandia Peak in 90 minutes.
Drag: Coefficient of drag in hp/(mph*3). The number you enter here is used for
calculating how much of your energy goes towards countering wind resistance.
The units are weird, but they come from the approximation that the energy
required is proportional to the cube of your velocity. A value of 3.5x10-5
appears to be a good value for riding a touring bike with your arms fairly
straight. (You only have to enter the 3.5. The program assumes the correct
value for the exponent.) For a hunched over racing position 3.0 is probably
reasonable, while straight up on a mountain bike you better use 4.0. A
little research wouldn't hurt here, but for the crude application here,
these values are probably OK.
How to enter values for the FRONT and REAR gears:
The rest of the blanks are for entering values for the number of teeth on the
front and rear sprockets of the bicycle's gears. There are several ways that
this can be done:
1. Direct entry:
Enter the number of teeth for each gear wheel directly on the line labeled
"Gear". For example a typical 10 speed bike would have two entries, say 52
and 42, entered for the front chainrings. The five sprockets on the
freewheel are entered in the table under "Rear", for example 14, 17, 20, 24
and 28. Note that the program expects the gears to be entered with the
highest gear first and then progressing to successively lower gears. Thus
for the front chain rings the numbers decrease, while for the freewheel
sprockets the numbers increase.
2. Minimum/maximum entry:
Lots of times you will want to try something like "how about a five sprocket
freewheel going from a 14 to a 32 tooth gear?" The GEAR program makes this
easy by allowing you to fill in 14 in position 1, blanks in positions 2, 3,
and 4, and then 32 in position 5. When you press the <Enter> key, GEAR will
fill in the blanks assuming as smooth a geometric progression as can be
accomplished with integral values for the number of teeth on each sprocket.
3. Percentage difference entry:
When you enter sprocket values explicitly, GEAR calculates the percentage
difference between every pair of values entered. (The Percent change is
displayed below each pair of gears.) If you wish, you can enter one explicit
value, say 14 for the first rear position gear, and then move down one line
to the Percent entry blanks. When you enter a value in a Percent field all
empty gear fields on the line above a filled in with the specified percent
change between each gear. For example, clear the Rear gear field using
<Ctrl-PgDn>, enter 14 in the first position, then move down a line and over
4 cells. Now enter 20 to get a five speed freewheel with approximately 20%
spacing between gears.
A note on "percentage differences" as calculated by GEAR:
How one calculates a percentage difference between two numbers X and Y depends
on whether you compare (X-Y) to Y or (Y-X) to X. If X is 10% larger than Y
(X=1.1Y) it is not true that Y is 10% smaller than X, although it's close.
To get a number that doesn't care how you do the comparison you have to get
tricky. The way I chose to get tricky was to calculate the difference in the
natural logarithyms of gears I was comparing, and then multiply by 100. The
result is a number that is equal to percent difference in the limit of small
differences, but with the advantage that these numbers can be added to get the
relative change over several gears. For what it's worth, that how it's done
here.
Playing the game:
Start out by entering what you have on your bike now. After getting a display of
the effective wheel diameter for each position of the front and rear gears,
check to see if the available gears are evenly spaced and give you the kind of
range you want. Then the fun begins: you play the game of trying different gear
combinations and see if you can improve the way your bike is set up. A few
weekends and $50 later you quit playing these games and get back to actually
riding your bike.
Notes on sub-directories:
In general it is assumed that all three GEAR files are contained in the current
default directory. The program can then be run by simply typing "GEAR" at the
DOS command line. Alternatively one can specify on the command line where the
program should look for the two data files. This is particularly useful on
hardisk systems where the data files are contained in a different subdirectory.