foggysps
12-14-2005, 08:42 PM
Circuit One Suspension
(503) 722-8475
Suspension Tuning Guide by Dave Hodges
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 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/Rear Shock - Race sag 25-30 mm, 1 - 1 3/16 inch
-Forks/Rear Shock - Street sag 30-35 mm, 1 3/16 - 1 3/8 inch
-Check chain alignment. lf not correct, sprocket wear is increased.
-Proper tire balance and pressure. If out of balance, there will be vibration in either wheel
-Steering head bearings and torque specifications, If too loose, head will 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
Forks: Adjustment Locations
=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.
Forks: Lack of Rebound
Symptoms:
-Forks are plush. but increasing speed causes loss of control and traction.
-The motorcycle wallows 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.
Typicalty after the first bump, the bike will skip over subsequent bumps.
-With acceleration, the front end will tank slap or shake violentty 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
Symptoms:
1/-Front end rides high through the comers, causing the bike to steer wide.
It should ride in the middle of suspension travel.
Solution:
* Too much compression. Decrease compression "gradually" until bike neither
bottoms or rides high.
2/-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 chaffering and shaking ceases.
3/-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.
4/- Ride is generally hard, and gets even harder when braking or entering turns.
Solution:
*Decrease compression 'gradually' until control is regained.
Shock : Adjustment Locations
-Rebound adjustment (if applicable) is located at the bottom of the
shock.
-Compression adjustment (if applicable) is located on the reservoir.
-Spring Preload 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 weavin 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 comers, due to rear squat.
It will slow steering because front end is tiding 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 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,bike
will tend to steer wide.
Solution:
* Insuficient 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:
* Too much compression.Decrease compression until harshness is gone.
decrease compression until sliding stops and traction is regained.
Stock Tuning Limitations:
New motorcycles purchased from the dealership are generally set-up on the soft side,
for a rider in the weight range of 140-165 lbs. If you are not in this range, you
must retune the suspension tor your weight within the internals of forks and shocks,
the manufacturer puts valve with small venturis. This, along with shims, creates a
damping curve. This works okay at slower speeds, but at higher speeds, when the
suspension must react more quickly, the method cannot low enough oil and you experience
hydraulic lock. With hydraulic lock, there is no damping. The fork and/or shock cannot
dampen correctly and handling suffers. The solution is to revalve the active components
for the proper damping curve. It does not matter what components you have, (Ohlins, Fox,
KYB, Showa). If you can achieve the damping curve that is needed, it does not matter what
brand name is on the component. Sometimes with stock components, when you turn the
adjusters full in or out, you do not notice a difference. This is due to the fact that
the manufacturer has put the damping curve in an area outside of your ideal range. After
revalving, the adjuster will be brought into play, and when you make an adjustment, you
will be able to notice that they effect the way the fork or shock perform.
One of the problems with stock springs is, in most cases, it is of a progressive rate.
This is to say, a spring at sag may be .85 kg per mm, and at 2.5 inches of travel, it may
be 1.05 kg per mm, getting progressively stiffer. The ideal solution is to install a sprig
with a straight rate, specific for your weight, and the weight of your motorcycle. In some
cases, the factory installs a straight rate spring, but often the incorrect rate for your
weight.
Dave W. Hodges
Circuit One Suspension