SUSPENSION 101 - From a gixxer.com post [unedited temporarily]

Introduction
Unfortunately there is no literature that can give you the perfect machine setup. Also suspension setup is individually dependent on the rider (style, preference) and track conditions, which vary from race to race. We can therefore only try to give you guidelines and ground rules for the chassis setup of your machine.

General guideline
The general guideline in road racing is that the suspension has to support the tires to create the best possible grip. For this reason suspension plays it's most important role in corners, chicanes, acceleration and braking. In the straight line the suspension works satisfactory if it can absorb the bumps without causing instability.

Suspension stroke
A road race bike should normally not use its full suspension stroke, although on some circuit one or two big bumps or hollows can cause the suspension to bottom. Also landing of front wheel after wheelies can cause excessive use of the front fork stroke. If suspension bottoms in big bump or hollow, it should not automatically mean that the suspension should be set harder. However, if suspension bottoms at the place were the maximum grip is essential the tire cannot create the best traction, because it also has to perform as spring. Adjusting the setting is necessary. During every riding session the suspension stroke should be carefully checked. When tire grip and lap times improve, the suspension has a harder job. So, setting must be set harder. On the opposite, when it starts raining tire grip and lap times go down, in that case a softer setting should be applied.

Suspension setup
Before starting suspension setup, read the owners manual!
A tip, do your changes in suspension setup one by one, try to learn what effect each individual adjustment has on your bike and take notes!

Static sag without rider
Hold the bike upright on a flat surface. Independently lift front and rear until the suspension is fully extended, the value should be approximately:

Type Front sag Rear sag
Super Bike 20-30 mm 5-10 mm
Super Sport 20-30 mm 5-10 mm
RR 250 15-25 mm 0-5 mm
RR125 15-25 mm Just top out 0 mm

Note: An RR 125 cannot afford to loose the momentum that the sag would give in a straight line (loss of top speed). The static sag is adjusted by the spring preload. The procedure is the same for the front fork and rear shock.

Static sag with rider
The accepted manner to adjust the spring ratio is to measure how much stroke is used with the rider sitting on the bike in straight line position (behind fairing) after you have set the correct static sag without rider. Normally 1/3 of the full stroke is a good starting point for all machines. This is only a guideline for the right spring ratio. The final check must be done on the circuit.

Note: Ohlins racing shocks features a "top-out" spring to prevent the shock from extending to quickly, causing the rear wheel to jump under braking. The top-out spring also effects the negative sag, making it difficult to adjust the sag with the shock on the bike.

Your Ohlins shock is delivered with the correct spring preload set and we recommend you to use this value for the basic setup. Ride height should be adjusted with the ride height adjuster on the bike or on the shock.

Rebound damping
*Rear suspension
Too much rebound damping can cause:
- The rear "jumps" on the bumps instead of following the surface.
- The rear "jutters" under braking.
- It holds the rear down with the result that the bike will understeer!
- It can cause overheating in the hydraulic system of the shock absorber and make it fade, in other words, it will loose damping when hot.

Too little rebound damping can cause:
- The rear "tops out" too fast under braking, causing the rear wheel to jump
- The bike feels unstable.

*Front suspension
Too much rebound damping can cause:
- Oversteering!
- It will give poor grip of the front tire.
- It feels like the front wheels will tuck under in corners.

Too little rebound damping can cause:
- Understeer!
- The front can feel unstable.

Compression damping
Rear suspension
Too much compression damping can cause:
- The rear wheel to slide under acceleration.
-It can give a harsh ride over bumps.

Too little compression damping can cause:
- The rear wheel start to bump sideways under acceleration out of the corner.
- The bike will squad too much (rear is too low), that will cause the front to loose grip.

Front suspension
Too much compression damping can cause:
- Good result during braking.
- Feels harsh over the bumps.

Too little compression damping can cause:
- Strong diving of the front.

Adjustment advice:
Compression damping should be adjusted together with front fork oil level.

Spring ratio
Rear
Too hard spring ratio:
- Gives easy turning into corners.
- Makes the rear feel harsh.
- Create poor rear wheel traction.

Too soft spring ratio:
- Gives good traction in acceleration.
- Creates understeer in entry of corner.
- Makes too much suspension travel, which will make it difficult to "flick" the bike from one side to the other in a chicane.
- Will give a light feeling in the front.

Front
Too hard spring ratio:
- Good under braking.
- Creates understeer.
- It feels harsh in the corners.

Too soft spring ratio:
- Gives easy turning into corners.
- Creates oversteer.
- Can cause front to tuck under.
- Bad under braking (diving).

Front fork oil level
First see manual. The modern front fork of cartridge type is very sensitive for oil Ievel changes, because of the small air volume Air inside the front fork works as a spring. The different level of oil affects the spring ratio from the middle of the stroke and has a very strong effect at the end of the stroke.

When the oil level is raised:
The air spring in the later half stage of travel is stronger, and thus the front forks harder.

When the oil level is lowered:
The air spring in the later half stage of travel is lessened, and thus the front forks are softer. The oil level works most effectively at the end of the fork travel.

Note: Adjust the oil level according to your manual.




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.

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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.


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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.


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Front Fork Problems
Possible Cure

Race sag too small -
Reduce preload.

Race sag too great -
Increase preload.

Forks compress too far on smooth turns -
Stiffer springs, increase preload.

Forks dive too far (bottom out) -
Stiffer springs, reduce air gap, possibly increase preload.

Always losing front end on corner entry -
Softer springs, adjust weight distribution.

Front end chatters coming out of corners -
Softer rebound springs or main springs, reduce damping.

Bike difficult to turn in -
Softer springs, reduce preload or compression damping, alter steering geometry

Front wheel skips on bumps -
Softer springs, reduce compression damping, increase air gap.

Forks judder when braking on a straight -
Reduce compression damping.

Forks dive too fast -
Increase compression damping.

Forks pump down on fast bumpy corners -
Reduce rebound damping.

Excessive pogo action through chicanes -
Slightly increase rebound damping.

Front end shakes (not chatters) in corners -
Increase rebound damping.

Front end shoots up too fast after braking -
Increase rebound damping.


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Rear Shock Problems
Possible Cure

Race sag too great -
Increase preload.

Race sag too small -
Reduce preload.

Rear squats on acceleration -
Stiffer spring, increase anti-squat angle, slightly increase compression damping.

Very Harsh ride over ripples -
Reduce compression damping.

Bike wallows -
Increase rebound damping.

Rear jacks up too fast on braking -
Increase rebound damping.

Rear end chatters exiting slow corners -
Increase rebound damping.

Bike kicks off ripples or bounces on bumps -
Increase rebound damping.

Rear end pumps down on bumpy corners -
Reduce rebound damping.




LACK OF COMPRESSION DAMPING ( Front Fork )

Front end dive while on the brakes becomes excessive.
Rear end of motorcycle wants to "come around" when using front brakes aggressively.
Front suspension "bottoms out" with a solid hit under heavy braking and after hitting bumps.
Front end has a mushy and semi-vague feeling, similar to lack of rebound damping.


TOO MUCH COMPRESSION DAMPING ( Front Fork )

Overly harsh ride, especially right at the point when bumps and ripples are contacted by the front wheel.
Bumps and ripples are felt directly - the initial hit is routed through the chassis instantly, with big bumps bouncing the tire off the pavement.
The bike's ride height is affected negatively - the front end winds up riding too high in the corners.
Brake dive is reduced drastically, though the chassis is upset significantly by bumps encountered during braking.


LACK OF REBOUND DAMPING ( Front Fork )

The fork offers a supremely plush ride, especially when riding straight up. However, when the pace picks up the feeling of control is lost. The fork feels mushy, and traction "feel" is poor.
After hitting bumps at speed, the front tire tends to chatter or bounce.
When flicking the bike into a corner at speed, the bike will tend to "porpoise" or wallow a bit, before settling down. Getting aggressive with the controls makes it worse. As speed increases and steering inputs become more aggressive, chassis attitude and pitch become a real problem, with the front traction feedback going numb after the bike is countersteered hard into a turn.


TOO MUCH REBOUND DAMPING ( Front Fork )

The ride is quite harsh - just the opposite of the plush feet of too little rebound. Rough pavement makes the forks feel as if they're locking up with stiction and harshness.
Under hard acceleration exiting bumpy corners, the front end feels like it wants to "wiggle" or "tankslap." The tire feels as if it isn't staying in contact with the pavement when on the gas.
The harsh, unforgiving ride makes the bike hard to control when riding through dips and rolling bumps at speed. The suspension's reluctance to maintain tire traction through these sections erodes rider confidence.



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LACK OF COMPRESSION DAMPING ( Rear Shock )

Too much rear end "squat" under acceleration - bike wants to steer wide exiting corners (since chassis is riding rear-low/nose-high).
Hitting bumps at speed causes the rear to bottom, which upsets the chassis.
Chassis attitude affected too much by large dips and "G-outs" - steering and control become difficult due to excessive suspension movement.


TOO MUCH COMPRESSION DAMPING ( Rear Shock )

Ride is harsh, though not quite as bad as too much rebound - however, the faster you go the worse it gets.
Harshness hurts rear tire traction over bumps, especially during deceleration.
There is very little rear end "squat" under acceleration.
Medium to large bumps are felt directly through the chassis - when hit at speed, the rear end kicks up.


LACK OF REBOUND DAMPING ( Rear Shock )

The ride is plush at cruising speeds, but as the pace increases, the chassis begins to wallow and weave through bumpy corners.
Poor traction over bumps under hard acceleration - rear tire starts to chatter due to lack of wheel control.
Excessive chassis pitch through large bumps and dips at speed - rear end rebounds too fast, upsetting chassis with a pogo-stick action.


TOO MUCH REBOUND DAMPING ( Rear Shock )

Very harsh ride - rear suspension compliance is poor and "feel" is vague.
Poor traction over bumps during hard acceleration (due to lack of suspension compliance).
Bike wants to run wide in corners since the rear end is "packing down" - this forces a nose-high chassis attitude, which slows down steering.
Rear end wants to hop and skip when the throttle is chopped during aggressive corner entries