This combination is commonly referred to as the shock absorber. Damping is divided into two parts. Compression Damping comes into play when the shock is compressed and helps absorb the impact when a bump is encountered and the wheel goes up. Rebound Damping controls the return of the shock absorber and wheel to its original position. If it returns too slowly the shock absorber may not allow the wheel to return to its correct position for the next bump causing the tire to lose contact with the road surface.
Control is the key word.
Rebound damping controls the speed is which the spring and damper combination return to its original position. Spring rates are selected by Progressive Suspension to match each motorcycle application. On those applications where you have a choice of a standard spring or a heavy duty spring, the heavy duty spring should be selected for a load weight over 200 lbs, not by how fast you ride. There are four common types of springs. A progressively wound spring will usually have coils closer together on one end producing a progressively stiffer spring rate.