Circuit One Suspension
SUSPENSION TUNING GUIDE - by Dave Hodges
FOR STREET OR ROAD RACING BIKES

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 first:

• 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. If 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.

TROUBLESHOOTING FORK DAMPING PROBLEMS

Fork 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.
• Typically after the first bump, the bike will skip over subsequent bumps.
• 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:

Symptoms

• Front end rides high through the corners, causing the bike to steer wide. It should ride in the middle of suspension travel.
• Front wheel bounces over bumps while ripples and bumps are felt directly in the triple clamps and through the chassis.
• Ride is generally hard, and gets even harder when braking or entering turns.

Solution

Too much compression - Decrease compression "gradually" until the bike neither bottoms or rides high, and control and traction are optimized.

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.

TROUBLESHOOTING SHOCK DAMPING PROBLEMS

Shock Adjustment Locations:

• Rebound adjustment (if applicable) is located at the bottom of the shock.
• Compression adjustment (if applicable) is located at the top of the shock or on the reservoir.
• Spring preload 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 down, 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

Too much compression - Decrease compression until harshness is gone. Decrease compression until sliding stops and traction is regained.

Tuning Limitations of Stock Parts:

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 for 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 re-valve 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 re-valving, the adjusters will be brought into play, and when you make an adjustment, you will be able to notice that they affect the way 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.

Remember to always make small adjustments, and keep notes! Sometimes more is not better and be patient. Suspension is an art/science.

A major issue with springs, front and rear, is to simply spring the ends so that when you push down on the footpegs (where most of your weight is when you aggressively corner). Both ends of the bike NEED to go up and down exactly evenly, both in travel and rate. That's without damping.

General order:
Select a rear spring that will just bottom out over your harshest bump with "normal" sag. Soften it up till it just bottoms out, then tighten preload 1/4. Check the sag and see if it's in general range of 35mm to 20mm.

Select front fork springs that allow the front end and the rear end to travel equally and evenly when you bounce on the footpegs (helps to have someone hold the bike upright). That's after you have set the rear spring as in the above step.

Rear rebound: Use just barely enough to prevent wallowing in high speed sweepers.

Front rebound: Use just enough rebound to keep the front end from wallowing when exiting low speed corners at full throttle.

Compression damping: The goal is to use as little as possible. Use the proper, perhaps heavier than stock spring to do the major work during non-raking mode riding.

Use compression damping to trim if necessary and only if required.

Excessive dive under braking: Use increased oil level to firm the front end under hard braking. 5mm is a significant change.

Goals are to always use the softest rear spring that works within "sag" range limit.

Use just enough rebound damping to control the springs.

Use as little compression damping as possible and only when required. Not everybody has a supply of alternate fork and shock springs, so you will probably have to improvise and use a bit of extra preload or a bit more compression damping to compensate for too soft of a spring.

All in all, there is nothing like heeling a bike over in a 120mph sweeper with a sharp edged bump in the middle of it and knowing that you can back of just a bit over the bump, get bounced in the air and calmly land heeled over, in control, straight and unperturbed and remain at highest possible speed with no fuss or muss.

That just doesn't happen if the springs aren't perfectly matched!

Cheers!
Marc

Remember! These are hints only.
You are responsible for whatever you do with this information.

If you use this information and it helps your application, contact Factory Pro with results. Thanks, Marc

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