How to Adjust a Motorcycle Shock Absorber

Update:22 Jun, 2023
Summary:The motorcycle shock absorber is the mechanism that eliminates much of the jarring road shock transm...
The motorcycle shock absorber is the mechanism that eliminates much of the jarring road shock transmitted to the rider and the wheel when traversing uneven surface conditions. A well-tuned and properly adjusted shock absorber is essential to rider comfort, handling performance, tyre grip, and a smooth road holding experience.
A shock absorber is not a spring; instead, it is a hydraulic system that converts the movement of the piston (in the most basic design) into heat by passing oil through it. This thermal energy is dissipated into the atmosphere, reducing the amount of kinetic energy transmitted to the chassis and rider from the wheel impacting the road surface.
Motorcycle springs, such as those found on both the front fork and rear shock, are under constant compression due to the vehicle's weight at all times; adding a rider or luggage adds even more to this load. Adjustments to this compression - also known as sag - can be made to the suspension with either the use of spring preload adjusters or by altering the ride height of the chassis via changing the distance from the fork tubes' center to the steering stem.
In order to achieve optimal suspension performance, the damping force of the shock absorber must be proportional to the shock-spring stiffness. Otherwise, a stiff spring will easily overpower the damping and cause a harsh ride.
Damping is provided by a valve or orifice that limits the amount of fluid flowing through the damper during its compression phase as the wheel lifts over a bump; this is known as the "plateau" effect. A damper with too little damping on compression will result in a harsh ride, particularly as the speed of travel increases; it will be difficult to maintain adequate traction through a bumpy section or when accelerating out of a corner.
On the other hand, a damper with too much rebound will allow the wheel to drop back down and bounce excessively after hitting a bump; this can be annoying for casual riders and especially for racing machines, which need to keep the front tire in contact with the ground as they accelerate out of corners.
Ideally, the free sag of the rear shock should be between 0 and 5mm when the bike is at rest. Street bikes, however, should have more sag than racers since they are heavier. Another issue is "packing," where the suspension compresses further down after each successive bump due to overly aggressive rebound damping. If this is occurring, the damping setting should be reduced gradually until the bike's geometry is corrected. See the article on rake for more information about this issue.