Motorcycle Suspension Setup: Getting to Grips with a Black Art
By Mark J Thompson
Suspension Set-up: The basics
Whether you are a road rider or a racer correct suspension setup is the key to fast smooth riding and consistent lap times. To get the best out of your bike it needs to be set up for the conditions in which you will be riding. It is considerably easier to set the bike up for the Track as you know what conditions will be like for the next hour or so and thus you can dial in the optimum settings for the that particular situation.
To what extent you change your suspension settings will depend on whether your bike will also have to cope with riding on the road. Unlike Roads Tracks are generally smooth and grippy. So if you are only going to use the bike on the track you have the luxury of fitting harder springs and modifying the fork and shock internals. If you ride on the road as well as the track you will probably want to keep a certain comfort level and concentrate on just optimizing the current equipment
With incorrect suspension setup, tire wear is increased and handling suffers, which in turn can result in rider fatigue. Lap times can be dramatically slower and in extreme cases safety can be compromised. Hopefully the following guide will help you dial in your suspension for faster and safer riding both on and off the track.
Firstly you will need to check the Fork and Shock sag: this is the amount the forks and rear shock settle under load. To measure it do the following: push down on the forks a number of times to settle them, then mark the stanchion with a felt pen or put a cable tie where the dust seal is sitting. Next ask some for help to lift on the bars so the front wheel is just off the ground and measure the amount the forks have traveled down. This is the static sag (or unladen sag), This can be changed by adjusting the spring preload (more preload = less sag). Repeat the same process for the rear, this time measuring the distance from the wheel spindle to a fixed point on the tail. Now you are ready to begin setting up your suspension. The key is to do it a little at a time and make notes as you go. For road riding start with the wet track settings and work from there.
Basic Setup: Check the following:
- Forks sag 18-22 mm for dry track, 23-27mm for rain.
- Shock sag 8-10mm for dry track, 10-14mm for rain.
- Check chain alignment. If not correct, bike will crab walk and sprocket wear will be increased.
- Proper tire balance and pressure, starting with 30psi front and 32psi rear (both dry and wet).
- 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.
Stock Suspension Tuning Limitations
Manufacturers plan on designing a bike that works moderately well for a large section of riders and usages. To accomplish this as economically as possible, they use 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, Kayaba, 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.
- Always make small adjustments, more is not always better.
- Always keep notes of what you have done.
- Suspension tuning is an art - be patient.
Mark Thompson has spent the last 20 Years Racing motorcycles and managing Race
Teams. He now runs the Trackbikes
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