Suspension Set-up and Adjustments

DISCLAIMER - This text is based on information found on the Internet. If you feel any of it is inaccurate, please contact me or Register and change it on the site. The whole purpose is to inform, not mislead. You are also reminded that this information, as all infromation on this site, is used at YOUR OWN RISK!

Introduction
This section will attempt to offer advise on how to best set up and adjust the suspension on your race bike. The whole purpose to setting up suspension properly is to maximise grip from the tyres, which ultimately leads to improved lap times. For this reason alone, your suspension will play its most important role during cornering, accelerating, and braking. Also, while in a straight line a well set up suspension will absorb bumps in the track without upsetting the stability of the bike.

Usually, the suspension won't use the entirety of its stroke, although on certain circuits it’s not unusual for the suspension to bottom out over a big bump or through a hollow. If your suspension does bottom out under these conditions, it doesn't necessarily follow the suspension should be set harder to compensate. However, if the suspension is bottoming out when maximum tyre grip is essential, for example apexing a fast corner, the tyre cannot offer its best grip because it is also acting as a spring, and adjustment will be necessary. Remember the golden rule... When tyres grip and lap times improve, the suspension has a harder job to do, so must be set harder. On the flip side of this rule, when it starts raining and tyre grip goes down, softer settings should be used.

Before Starting
Before starting to set up your suspension, it’s always a good idea to read the manuals. This way you'll best understand what adjusters have what effect on the suspension internals. Blindly fiddling adjusters will leave you with nothing but a bike that is all but impossible to ride effectively. Also, before starting to maximise your settings, the following should be checked:

1. Check chain alignment. If the drive chain is out of alignment sprocket wear will be accelerated, but more important you will lose power at the rear wheel!
2. Check proper tyre pressures and wheel balance. If tyre pressures are too low or too high, stability is compromised and tyre wear is accelerated.
3. Check steering head bearings are adjusted properly. Loose head bearings will compromise stability and give false feedback as to what the front end is doing.
4. Check front-end alignment, ensuring the fork geometry is correct. If your forks are out of alignment, they will compromise stability, giving false feedback as to what they are doing, and also have an adverse effect during turning-in and cornering.
5. Check proper frame geometry. Similar to front-end misalignment, only more so.

Suspension Hardware

Once you are happy all the above is okay, you should now consider your current suspension hardware. Most bike manufacturers fit suspension components that are more than sufficient for the road, but unfortunately, they just won’t be good enough for race use. Also, they fit a “one size fits all” set of components. At the very least, you should consider replacing the springs in the forks. Springs are graded by weight, and when buying replacements, normally you would tell the supplier of your kitted weight, i.e. how much you weigh with your leathers and helmet on, and they will supply you with a spring to suit. When buying replacement springs, make sure you get “linear” rather than “progressive” ones also.

Similarly, the rear shock absorber would be replaced using the same guideline. Most, if not all, aftermarket shocks have compression damping, which give you better control of the whole suspension stroke. Older shocks fitted as standard on the NC30/35s, ZXRs, FZRs, etc. only allow for rebound damping. One last consideration when buying a replacement rear shock should be ride height adjustment. It is highly recommended you buy a shock with this adjustment.

Now you have decided on the suspension hardware you are going to use, it’s time to start considering how best to utilise it.

First off, you should set up the static sag, both front and rear. To do this is fairly simple. You should aiming to set the sags as below:

Note - The RR125 class of bike cannot afford to lose the momentum that the rear sag would give in a straight line.

Setting Front Sag
To set the front sag, make sure the bike is held upright on a flat surface. Before making any adjustments and measurements, it’s a good idea to let off any rebound damping and compression damping (if available). First off you should lift the front wheel clean off the ground, allowing the forks to fully extend. This is best achieved by using a paddock stand which lifts the bike at the headstock. Next, using a cable tie or similar, wrap this around the fork stanchion (i.e. the silver chromed bit, NOT the outer fork leg) and push it all the way down the stanchion so it rests against the fork leg dust seal. Next, gently let the front wheel back down and let the front settle. You shouldn’t bounce the forks or put any extra weight on the bike at this point. The idea is to let the weight of the bike and nothing more compress the forks. Now you need to lift the front wheel again clean off the floor. As the weight comes off the front, the cable tie will remain in place and the fork leg will extend again. This lets you measure the distance between the cable tie and the dust seal. If the recorded distance falls between the readings in the above table, its fair to assume the sag is close to what you are looking for. If you find the reading is less than the minimum value stated, then the preload on the spring is too much, and should be let off. Similarly, if the reading is more than the maximum value stated, the spring preload is too little and should be increased accordingly.

Adjustment of the spring preload is carried out by using adjuster on the top of the fork. Just as a note of caution, always adjust both forks at the same time and by the same amounts! One full turn clockwise will increase preload, hence reducing sag, by approximately 3 millimetres*, and vice versa when turned anti-clockwise.

Finally, I’ll point out that it is worth carrying out the measurement a number of times to take into account small errors which can be made when letting the weight down on the front wheel again. Don’t settle for one reading – check it and check it again until you get some consistency from a number of readings.
Note - 3 millimetres is the rate at which one full turn adjusts the sag on the Honda NC30. Different manufacturers may use different ratios.

Setting Rear Sag
Once you’re done with the front sag, you should move onto the rear sag. The set-up procedure is very similar to the front, but you will need to call on assistance. Alternatively, a workshop stand, which facilitates lifting the rear wheel clear of the ground, should be sourced. Again, to set the sag on the rear shock, the shock has to be fully extended with no weight at all on it.
Before starting, identify a suitable position on the subframe of the bike and on the rear spindle, onto which you should make two reference marks. Ideally, these two points should be a close to the vertical as possible. Have your assistant lift the rear end of the bike until the rear wheel is clear of the ground, ensuring no weight is on the shock, thus letting it fully extend. Now you should measure the distance between your two reference points. Next, let the weight of the bike come down gently onto the rear wheel. Measure again the distance between your two reference points. The difference found is your rear static sag. If the recorded distance falls between the readings in the above table, its fair to assume the sag is close to what you are looking for. If you find the reading is less than the minimum value stated, then the preload on the spring is too much, and should be let off. Similarly, if the reading is more than the maximum value stated, the spring preload is too little and should be increased accordingly.

Adjustment of the spring preload is usually by either a castellated nut and locknut or by a series of stepped indents on an adjusting ring. Irrespective of the adjuster fitted, to increase the preload you will turn the adjuster clockwise, and vice versa to decrease the preload. The castellated nuts appear to be more common on aftermarket shocks as they allow for a greater degree of accuracy when setting preloads. Again, once you have adjusted and set the preload it is worth checking the measurements a couple times just to ensure you find consistent readings.

If after setting the front and rear sags, you find that no amount of preload adjustment can let you find a setting within the required ranges, chances are the springs or shock fitted are totally wrong for your bike. At this point, you’ll need to change them.

Static Sag with Rider
Once you are happy you have the static sags set up accurately, you should now consider checking the sags while you are sat of the bike. Put simply, this involves checking the suspension travel found while sat on the bike fully kitted and in the crouched position/riding position. There are no hard and fast measurements to be taken here, but as a rule you should find the travel is approximately one third of the total travel available. If you find this is close, it’s a good indication the springs fitted to the forks and the shock are a good match to our weight, and fine adjustment of rebound and compression damping should be more productive.

Finally, it should be noted the ride height is altered when adjustments to spring preloads are made. Ride height affects the geometry of the steering angle, or rake angle, of the front forks. This in turn affects the speed at which the bike will turn in to corners. There are a number of ways in which the ride height can be restored after preload adjustments, for example a jack up kit, or raising or lowering the front forks through the triple clamps. These methods may have the detrimental effect of lowering available ground clearance, so the preferred method is to use the ride height adjuster on your aftermarket rear shock.

One other advantage to this is to aim towards bettering the rake angle. Most bikes, such as the NC30 or the ZXR, have a quite conservative rake angle of 24.5 degrees or so. Thoroughbred race bikes, such as the RC45 or the Ducati 916/996 family have a far more aggressive 23.5 degrees. Again, through the use of ride height adjustment, you can aim towards this more aggressive rake angle without compromising stability but gaining quicker turning in characteristics.

Cause and Effects
Unfortunately, this is as much as I can offer with regards to searching for the perfect set-up, as tuning suspension is wholly dependant on a number of factors including rider style and preference. To this end, I will now describe what you can expect to feel on the track, and how to go about “dialling it out”.

Spring Rates
Front Springs too hard -

• Will be good under braking

• Creates Understeer

• Will give harsh feedback

Front Springs too soft -

• Will dive heavily under braking

• Creates Oversteer

• Allows for easy turning-in into corners

• Can lead to front tucking under while cornering

Rear Spring too hard -

• Allows for easy turning into corners

• Will give harsh feedback

• Creates poor rear wheel traction

Rear Spring too soft -

• Creates good traction under acceleration

• Creates Understeer

• Makes bike difficult to “flick” from side to side in chicanes

• Creates a light feeling on the front end

Rebound Damping - controls the rate at which the springs are allowed to return to their normally extended state after compression.
Front Suspension too much Rebound Damping

• Creates Oversteer

• Creates poor grip by the front tyre

• Can lead to front tucking under while cornering

Front Suspension too little Rebound Damping

• Creates Understeer

• Creates a light feeling at the front end

Rear Suspension too much Rebound Damping

• The rear tyre “jumps” on bumps, rather than following the surface of the track

• The rear tyre “jitters” under braking

• Creates Understeer

• Can cause overheating of the shock hydraulic system, causing fade, leading to loss of damping when hot

Rear Suspension too little Rebound Damping

• The rear tops out too fast under braking, causing the rear tyre to jump

• The whole bike feels unstable

Compression Damping - controls the rate at which the springs are allowed to compress during compression.
Front Suspension too much Compression Damping

• Good results under heavy braking

• Harsh feeling over bumps

Front Suspension too little Compression Damping

• Strong diving at the front under braking

• Front end feels soft and vague, similar to too little rebound damping

Rear Suspension too much Compression Damping

• Loss of traction causing rear wheel to slide under acceleration

• Harsh feeling over bumps

Rear Suspension too little Compression Damping

• Rear wheel will start to bump out under acceleration out of corners

• Rear end will squat too much, causing a loss of grip at the front wheel

As not all bikes have compression damping on the front forks, a certain amount of compression damping can be gained by adjusting the fork oil levels. Modern cartridge-type front forks can be reactive to adjustments in the oil levels, but it should be noted the greatest damping effects tend to occur towards the end of the stroke.

When the oil level is raised, the air spring in the latter stages of travel is stronger, thus the forks are harder. Similarly, when the level is lowered, the air spring effect is lessened and the forks are softer.