Introduced on bicycles in the early 1990s, suspension forks were designed to absorb impact from rocks, fallen tree limbs, and other obstacles encountered on the trail. A full suspension mountain bike includes not only a suspension fork, but also a rear shock. The principle is the same: the coil shock reduces road impact felt by the rider. A pair of adjustments is crucial to the operation of the shock and to personal ride quality. The first adjustment, “preload," determines how much the shock sags under normal rider weight. The second, “damping," affects how quickly the shock rebounds after compressing.
Use a measuring tape to measure the distance from the center of one of the shock’s mounting bolts to the other. There is a mounting bolt at each end of the shock. Remember this measurement.
Sit atop the mountain bike and assume your normal riding position. You may have to hold onto the side of a wall for support.
Remain seated. Have an assistant measure the distance between the mounting bolts once again.
Subtract the second measurement from the first. The difference should be approximately one-quarter the length of the original measurement. If the difference is greater than one-quarter of the original measurement, the preload is set too low. If the difference is lower, the preload is set too high.
Look for a preload collar at top end of the shock. To set a higher preload, turn the preload collar once toward the coil. To set a lower preload, turn the preload collar once away from the coil.
Mount the bicycle, and have an assistant once again measure the distance between the shock’s mounting bolts. Adjust the preload collar setting again, as needed, until the preload is correct.
Take the mountain bike for a ride. Choose your normal riding area. The riding area should include any conditions typically encountered on an average ride.
Note the “feel” of the shock as it rebounds from bumps. If the rebound feels abrupt, the damping is set too high. If the rebound feels soft or slow, the damping is set too low. There’s no universal setting. Ideal rebound damping depends on road conditions, rider style and rider weight.
Look for a dial near the bottom end of the shock. Turn the dial clockwise once to soften damping and slow the return of the shock. Turn the dial counter-clockwise once to cause the shock to rebound faster.
Continue to ride the bike to check the damping adjustment. Adjust further if necessary, until the damping setting feels comfortable.