Yamaha FZR400 1988-1989, Service Manual

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The main reasons to adjust ride height are to change the steering geometry of the motorcycle or to
change the ground clearance of the motorcycle. Raising the rear ride height steepens the steering head
angle; lowering the rear ride height slackens the steering head angle.
If the cornering clearance on your motorcycle is too low, increasing the rear ride height can reduce the
problem. On the other hand, you can lower the seat height by reducing the rear ride height.
NOTE: Most motorcycles were not designed with length-adjustable shocks in mind. Be careful when
changing the shock length. Make sure that moving parts like the wheel, swingarm, and fender do not
contact the motorcycle chassis at the limits of travel.
The handling of the motorcycle could be adversely affected by changing the rear ride height. Also,
decreasing rear ride height will reduce the cornering clearance of the motorcycle.
It is very important that you do not wind out the threaded adjuster more than is shown in Figure 2; do
not exceed 0.430 (11 mm) as there will not be enough threads left in the shock absorber and the results
could be disastrous.
The shock length may be adjusted while the shock is mounted to the motorcycle. To adjust, place the
bike on a stand so the wheel is in the air and the suspension is unloaded. Loosen the jam nut and turn
the extension. The eyelet or clevis at the lower end of the shock will remain stationary and the shaft will
rotate inside the shock. Be sure to take note of the above warnings.
Here are a few examples of how changing the rear ride height can affect your motorcycle performance:
Symptom Problem
Motorcycle is unstable at high speeds
Rear Ride Height too high
Poor grip from rear tire Rear Ride Height too high
Unstable under heavy braking Rear Ride Height too high
Motorcycle understeers on exit corners Rear Ride Height too low
Difficult to change direction Rear Ride Height too low
Poor grip on front tire on exit corners Rear Ride Height too low
When to adjust Ride Height vs. Spring Preload
You may ask, “How is adjusting shock length different from adjusting spring preload? Don’t they both
affect ride height?” The answer – yes, they both affect ride height, but changing spring preload has
other side effects.
In a nutshell, spring preload only sets the amount of compression and extension travel available.
When you increase spring preload, you also increase the rear ride height, but at the cost of reduced rider
sag. Reducing rider sag will make your shock more likely to top out.
Similarly, reducing spring preload decreases rear ride height, but at the cost of increased rider sag.
Increasing rider sag will make your shock more likely to bottom out.
Changing ride height gives you independent control over ride height and travel. For example, suppose
you needed to increase the rear ride height to improve cornering clearance. On a stock shock absorber,
you would have no choice but to increase spring preload, making the shock top out more often and
decreasing ride quality. Changing the shock length could allow you to increase cornering clearance
while still maintaining proper travel.