Motorcycle suspension-mastering a black art
Suspension Set-up: The basics
Whether you are a road rider or a racer correct suspension setup
is the key to fast smooth riding and consistent lap times. To
get the best out of your bike it needs to be set up for the
conditions in which you will be riding. It is considerably
easier to set the bike up for the Track as you know what
conditions will be like for the next hour or so and thus you can
dial in the optimum settings for the that particular situation.
To what extent you change your suspension settings will depend
on whether your bike will also have to cope with riding on the
road. Unlike Roads Tracks are generally smooth and grippy. So if
you are only going to use the bike on the track you have the
luxury of fitting harder springs and modifying the fork and
shock internals. If you ride on the road as well as the track
you will probably want to keep a certain comfort level and
concentrate on just optimizing the current equipment With
incorrect suspension setup, tire wear is increased and handling
suffers, which in turn can result in rider fatigue. Lap times
can be dramatically slower and in extreme cases safety can be
compromised. Hopefully the following guide will help you dial in
your suspension for faster and safer riding both on and off the
track. Firstly you will need to check the Fork and Shock sag:
this is the amount the forks and rear shock settle under load.
To measure it do the following: push down on the forks a number
of times to settle them, then mark the stanchion with a felt pen
or put a cable tie where the dust seal is sitting. Next ask some
for help to lift on the bars so the front wheel is just off the
ground and measure the amount the forks have traveled down. This
is the static sag (or unladen sag), This can be changed by
adjusting the spring preload (more preload = less sag). Repeat
the same process for the rear, this time measuring the distance
from the wheel spindle to a fixed point on the tail. Now you are
ready to begin setting up your suspension. The key is to do it a
little at a time and make notes as you go. For road riding start
with the wet track settings and work from there. Basic Setup:
Check the following Forks sag 18-22 mm for dry track, 23-27mm
for rain. Shock sag 8-10mm for dry track, 10-14mm for rain.
Check chain alignment. If not correct, bike will crab walk and
sprocket wear will be increased. Proper tire balance and
pressure, starting with 30psi front and 32psi rear (both dry and
wet). Steering head bearings and torque specifications - if too
loose, there will be head shake at high speeds. Front-end
alignment. Check wheel alignment with triple clamps. If out of
alignment, fork geometry will be incorrect and steering will
suffer. Crash damage, check for proper frame geometry. Stock
Suspension Tuning Limitations Manufacturers plan on designing a
bike that works moderately well for a large section of riders
and usages. To accomplish this as economically as possible, they
use valving with very small venturis. These are then matched to
a very basic shim stack which creates a damping curve for the
given suspension component. At slower speeds this design can
work moderately well, but at higher speeds, when the suspension
must react more quickly, the suspension will not flow enough
oil, and will experience hydraulic lock. With hydraulic lock,
the fork and/or shock cannot dampen correctly and handling
suffers. The solution is to re-valve the active components to
gain a proper damping curve. It does not matter what components
you have, (Ohlins, Fox, Kayaba, Showa) matching them to your
intended use and weight will vastly improve their action.
Furthermore, if you can achieve the damping curve that is
needed, it does not matter what brand name is on the component.
Often with stock components, when you turn the adjusters full in
or out, you do not notice a difference. In part, this is due to
the fact that the manufacturer has put the damping curve in an
area outside of your ideal range. Also, because the valves have
such small venturis, the adjuster change makes very little
difference. After re-valving, the adjusters will be brought into
play, and when you make an adjustment, you will be able to
notice that it affects the way the way the fork or shock
performs. Another problem with stock suspension is the springs
that are used. Often they are progressive, increasing the spring
rate with increased compression distance. This means that the
valving is correct for only one part of the spring's travel, all
other is compromise. If the factory does install a straight-rate
spring, it is rarely the correct rate for the weight of the
rider with gear. The solution is to install a straight-rate
spring that matches the valving for the combined weight of the
bike, rider and gear to the type of riding intended. Remember!