The primary function of shock absorbers is to control the oscillation of the vehicle’s springs when the vehicle travels over bumps in the road. This makes for a more comfortable ride for the vehicle’s passengers, improves braking and handling, and limits wear and tear on the vehicle’s suspension and tires. Shock absorbers are bolted between the vehicle’s suspension and its frame, and sometimes incorporate the springs, sometimes not. Here is a typical example:
Shock absorbers control the oscillation of the spring by forcing hydraulic fluid inside the shock tube through a series of valves. Over time these valves wear out, resulting in poor handling and ride comfort.