Suspension Tuning Guide
Street Bike or Road Racing Applications
With incorrect suspension setup, tire wear is increased and handling suffers,
resulting in rider fatigue. Lap times can be dramatically slower and overall
safety for both street and race enthusiasts is another issue. Add the
frustration factor and it just makes sense to properly setup your suspension.
The following guide will help you dial in your suspension for faster and safer
riding both on and off the track.
Basic Setup: Check the following
Forks sag 25-40 mm
Shock sag 25-35 mm
Check chain alignment. If not correct, bike will crab walk and sprocket wear
will be increased.
Proper tire balance and pressure. If out of balance, there will be vibration and
headshake.
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.
Adjustment Locations on Forks
Rebound adjustment (if applicable) is located near the top of the fork.
Compression adjustment (if applicable) is located near the bottom of the fork.
Spring preload adjustment (if applicable) is generally hex style and located at
the top of the fork.
FRONT FORKS:
Forks: Lack of Rebound
Symptoms:
Forks are plush, but increasing speed causes loss of control and traction
The motorcycle wallows and tends to run wide exiting the turn causing fading
traction and loss of control.
When taking a corner a speed, you experience front-end chatter, loss of traction
and control.
Aggressive input at speed lessons control and chassis attitude suffers.
Front end fails to recover after aggressive input over bumpy surfaces.
Solution:
Insufficient rebound. Increase rebound "gradually" until control and traction
are optimized and chatter is gone.
Forks: Too Much Rebound
Symptoms:
Front end feels locked up resulting in harsh ride.
Suspension packs in and fails to return, giving a harsh ride. Typically after
the first bump, the bike will skip over subsequent bumps and want to tuck the
front.
With acceleration, the front end will tank slap or shake violently due to lack
of front wheel tire contact.
Solution:
Too much rebound. Decrease rebound "gradually" until control and traction are
optimized.
Forks: Lack of Compression
Symptoms:
Front-end dives severely, sometimes bottoming out over heavy bumps or during
aggressive breaking.
Front feels soft or vague similar to lack of rebound.
When bottoming, a clunk is heard. This is due to reaching the bottom of fork
travel.
Solution:
Insufficient compression. Increase "gradually" until control and traction are
optimized.
Forks: Too Much Compression
Symptom:
Front end rides high through the corners, causing the bike to steer wide. It
should maintain the pre-determined sag, which will allow the steering geometry
to remain constant.
Solution:
Decrease compression "gradually" until bike neither bottoms or rides high.
Symptom:
Front end chatters or shakes entering turns. This is due to incorrect oil height
and/or too much low speed compression damping.
Solution:
First, verify that oil height is correct. If correct, then decrease compression
"gradually" until chattering and shaking ceases.
Symptom:
Bumps and ripples are felt directly in the triple clamps and through the
chassis. This causes the front wheel to bounce over bumps.
Solution:
Decrease compression "gradually" until control is regained.
Symptom:
Ride is generally hard, and gets even harder when braking or entering turns.
Solution:
Decrease compression "gradually" until control is regained.
REAR SHOCK:
Adjustment Locations on Shocks
Rebound adjustment (if applicable) is located at the bottom of the shock.
Compression adjustment (if applicable) is located on the reservoir. Spring
prelude is located at the top of the shock.
Shock: Lack of Rebound
Symptoms:
The ride will feel soft or vague and as speed increases, the rear end will want
to wallow and/or weave over bumpy surfaces and traction suffers.
Loss of traction will cause rear end to pogo or chatter due to shock returning
too fast on exiting a corner.
Solution:
Insufficient rebound: Increase rebound until wallowing and weaving disappears
and control and traction are optimized.
Shock: Too Much Rebound
Symptoms:
Ride is harsh, suspension control is limited and traction is lost.
Rear end will pack in, forcing the bike wide in corners, due to rear squat. It
will slow steering because front end is riding high.
When rear end packs in, tires generally will overheat and will skip over bumps.
When chopping throttle, rear end will tend to skip or hop on entries.
Solution:
Too much rebound. Decrease rebound "gradually" until harsh ride is gone and
traction is regained. Decrease rebound to keep rear end from packing.
Shock: Lack of Compression
Symptoms:
The bike will not turn in entering a turn.
With bottoming, control and traction are lost.
With excessive rear end squat, when accelerating out of corners, the bike will
tend to steer wide.
Solution:
Insufficient compression. Increase compression "gradually until traction and
control is optimized and/or excessive rear end squat is gone.
Shock: Too Much Compression
Symptoms:
Ride is harsh, but not as bad as too much rebound. As speed increases, so does
harshness.
There is very little rear end squat. This will cause loss of traction/sliding.
Tire will overheat.
Rear end will want to kick when going over medium to large bumps.
Solution:
Decrease compression until harshness is gone. Decrease compression until sliding
stops and traction is regained.
Stock Tuning Limitations
The factories plan on designing a bike that works moderately well for a large
section of riders and usages. To accomplish this as economically as possible,
manufacturers install 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, KYB, 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
Always make small adjustments, more is not always better.
Always keep notes.
Suspension tuning is an art, be patient. I hope you all find this helpful. Feel
free to email your questions to us at
info@mototechnw.com. We are always happy
to help inprove your ride. Herb Varin
