Video Suspension Tuning Suspension tuning can be a mystery for both the rider and his mechanic. As a rider on race day, you go out for your practice session and your suspension nearly kills you! You come back to the pits and your mechanic asks you if the high-speed rebound feels too fast? You haven't got a clue because for the last 20 minutes you tried to keep your motorcycle on two wheels! After riding and tuning motorcycles for years, I still cannot diagnose suspension problems by riding or watching the bike on a racetrack.

The best suspension tuners in the world have a well-developed sense of high-speed vision. They can watch a bike and rider on various sections of the track to determine how well the four different suspension circuits are working. Some suspension tuners are starting to encourage riders to make video samples for review.

You can acquire that same sense of high-speed vision with the help of a video camera. After video-taping the rider attacking various sections of the track, you can replay the tape one frame at a time and see exactly how the four different suspension circuits damp the impacts of jumps, whoops, and other track irregularities.

This section tells you how to use videotape to tune your suspension. First, I'll explain the four suspension circuits and the track sections that help isolate each circuit. At the end of this section is a troubleshooting chart that will help you to identify problems with each circuit. A suspension-data log sheet is also provided so you can record all the pertinent information on your bike and have the data reviewed by a suspension-tuning expert. The data log will help you to develop a mental framework for setting up your suspension properly. Finally, I will explain what changes suspension tuners make during revalving. A warning though: Do not try to revalve your own suspension! One small mistake can put you over the bars! First, set up your suspension with the proper springs, settings, oil heights, and so on. If you still need revalving performed, at least then you will know exactly what your suspension needs. Too many people have their suspension parts revalved without first trying to set up the bike properly.

Tuning with the Damping Circuits

As previously mentioned, the four suspension circuits of the forks and shock are the high-speed compression (HSC), high-speed rebound (HSR), low-speed compression (LSC), and low-speed rebound (LSR). Your main objective in video suspension tuning is to make video samples of the rider on sections of the track that best isolate two of these circuits at a time. Before you start riding and taping, change the suspension fluids, grease the linkage, and have the proper spring rates and sag settings on the shock and forks.

Low-Speed Compression (LSC) and Low-Speed Rebound (LSR) Tuning The low-speed circuits work in two common track sections, braking for tight turns and accelerating on a straight with far-spaced, shallow whoops. When taping a rider, be sure to have the whole bike and part of the ground in the film frame. Stand far enough back from the track section and pan with the rider for at least 25 yards. Replay the tape one frame at a time and pay attention to how the wheel follows the ground as the bike hits the bumps. The wheel shouldnít compress quickly or rebound abruptly. All Japanese dirt bikes have suspension adjusting screws that affect the low-speed circuits only. Turning the adjusting screws clockwise will increase the damping and slow/stiffen the low-speed circuit. Turning the screws counterclockwise will decrease damping and speed-up/soften the low-speed circuit.

High-Speed Compression (HSC) and High-Speed Rebound (HSR) Tuning The high-speed circuits work in two common track sections, landing from big jumps and accelerating on a straight with tightly spaced, sharp-edged whoops. Video a rider as he lands from a big jump, and for about 15 yards after he lands. That is important because there are usually many small bumps in the landing path after a big jump. Replay the tape one frame at a time and watch to see how equally both the front and rear suspension compress and rebound. If the rear shock rebounds too fast, the rear end may spring up so fast that it loads the forks. If both ends rebound too fast, the whole bike may spring up off the ground. That can be hazardous if there is a turn after the jump.

When taping in whoop sections, try to pan the rider in as much of the section as possible. Watch how the suspension reacts to the sharp-edged whoops at speed. The rear wheel shouldnít pack-up. Packing is caused when the HSC and HSR are too slow to react to the terrain. The wheel will stay compressed as it hits the next whoop. Eventually the rider loses control and must slow down. Taping in whoops also helps the rider; if the bike is reacting properly, he may gain enough confidence to go faster through the section

If the video tape indicates that you need to change the high-speed circuits, you must take the suspension to an expert in revalving because there are no external adjustments that you can make to the high-speed circuits.