home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Mac100% 1999 April
/
MAC100-1999-04.ISO.7z
/
MAC100-1999-04.ISO
/
Best Game Library
/
Dirt Bike 3D
/
Manual
/
Bikes
next >
Wrap
Text File
|
1999-01-10
|
8KB
|
171 lines
Designing the Ultimate Bike
No single bike design is the ultimate for all tracks.
The following section will explain the effects of
various bike properties on bike performance. With
this information and a little experimentation, you
should be able to design bikes for all types of tracks. Of course, you then have to learn to ride them.
Power and Weight
This one is simple. To make the fastest bike possible,
you always want maximum power and minimum weight. To
minimize the weight, minimize the bike weight, the
front wheel weight, and the rear wheel weight.
Brake power determines how much braking occurs when
you bring your throttle down to decelerate. You will
probably want to set this at it's maximum value so
that you can slow down as quickly as possible.
Bike Geometry
This requires a little more thought. The parameters
that affect overall bike geometry are front and rear
wheel radius, front and rear distance, front and rear
height, and rake angle.
In general, you want the center of gravity (the
location of the weight of the bike) to be as low as
possible. A top heavy bike tends to flip over more
easily (especially when you try to accelerate quickly).
So front and rear height should be kept as low as
they go. The only reason to increase these values
might be for appearance sake (e.g. creating a tall
"Monster Bike").
A large wheel radius tends to roll over small bumps
easier, but a large radius make the entire bike taller
and hence raises the center of gravity, which works
against you.
The front and rear distance determine how far the
front and rear suspension and wheels are located from
the center of the bike. Increasing these values tends
to make the bike more stable for two reasons. First,
increasing the wheel base makes the geometry inherently
more stable because it moves the points that contact
the ground farther from the center of gravity. Second,
increasing the wheel base increases the moment of
inertia of the bike which makes the bike more
difficult to rotate. Keep in mind that a stable bike
may not always be what you want. Increasing the moment
of inertia decreases the "gyration" effect which is
explained in "Riding Tips". A simple and important
fact to remember is that increasing the rear distance
allows you to accelerate faster without flipping over
backwards.
The rake angle is the angle between the frame and the
front suspension. A "chopper" usually has a very high
rake angle, which makes the bike look cool, but doesn't
help the handling very much. A lower rake angle allows
the front suspension to absorb the bumps in a vertical
direction better (which is the direction that most of
the bumps affect the suspension), but you also want to
absorb the bumps in a horizontal direction as you run
into them, so some rake angle is usually desired.
You'll have to play with this.
Suspension
This probably the most important aspect to designing
the ultimate bike (and also the most difficult) is the
suspension. The suspension consists of the front and
rear travel, the front and rear spring rates, the front
and rear compression damping, and the front and rear
rebound damping. The wheel weights also affect the
suspension, but as mentioned above, it is gererally
best to have these weights set to their minimum values.
When designing suspension for a particular bike, there
are some general concepts to keep in mind. The first
goal is to keep the rear wheel in contact with the
ground as much as possible since acceleration is caused
by the power transfer between the wheel and the ground.
Second is that you want to use all of the suspension
that you have. In general, you want the suspension to
"bottom out" (you hear a "clank" when it bottoms out)
once or twice in a race. This way, you know you are
using all of the available stroke. If it bottoms too
much, your suspension is too soft and if it doesn't
bottom at all, it might be too stiff.
The suspension travel is the distance that the wheel
can travel up and down. For a motocross bike, you
generally want this to be as large as possible so the
suspension can do the best job at absorbing bumps and
the impact from high jumps. Increasing the travel
raises the center of gravity, however, so you will
want to bring the travel down when designing a drag
bike, a hill climb bike, or a trials bike.
The spring rate is the stiffness of the spring that
the suspension rides on. A higher spring rate will be
able to absorb the impact from large bumps and high
jumps better, but a lower spring rate will allow the
suspension to absorb small bumps better. Keep in mind
that if you lower the suspension travel, you will
probably have to increase the spring rate since the
spring has less distance in which to do it's job.
If you have a suspension with springs and no damping,
the bike will just bounce like a pogo stick. For fun,
you can try this by setting all damping to zero. In a
real bike, damping is done by the oil in the shock
absorber. As the suspension compresses and rebounds,
the shock resists, or damps, the motion. If you push
down on the hood of your car and then let up, the car
should come back up and stop. If your shocks are bad,
it might bounce up and down a few times. If you had no
shocks, it would bounce up and down and up and down for
a long time.
The difference between compression damping and rebound
damping are when they work. Compression damping works
when the suspension is being compressed and rebound
damping works when the spring is pushing the suspension
back out. If your rebound damping is set too high,
the suspension will compress when you hit a bump, but
the damping will keep the suspension from recovering
(the wheel coming back down) before you hit the next
bump. In an ideal situation, you would want the wheel
to be all the way down for each bump.
Compression damping resists the compressing motion of
the suspension. It acts to stiffen the suspension,
like the spring rate does, but since it's not a spring,
it doesn't help to provide the force to push the
suspension back out.
The trick to designing the ultimate suspension is in
finding the proper balance between spring rate,
compression damping, and rebound damping. Trial and
error is often the best teacher. Keep in mind the goal
of keeping the rear wheel in contact with the ground as
much of the time as possible.
Gear Ratios
Gear ratios determine the relative speeds between the
engine and the rear wheel when you are in a particular
gear. The most important setting to adjust is probably
the ratio for the highest gear. The higher you set it,
the faster your bike can ultimately go on a flat
surface, but the higher you go, the less torque you can
generate to accelerate your bike. This is why lower
gears have lower ratios. You use those lower gears to
get the torque you need to get the bike moving, then
switch to the next gear when you start to run out of
engine speed in that gear. The gear ratios should be
spaced so that you can increase speed from one gear to
the next.
Auto/Manual Transmission
If you turn off auto transmission, you will have to shift
the bike yourself using the X and Z keys. The first time
you press the X key, the motor will start. The next time
you press it, you will shift into first gear. The race
will start one second after your motor starts, but you
won't be able to shift into first until the race starts.