Shock Absorbers — What They Actually Do

This is one of the most misunderstood components in suspension. Shock absorbers do not support the vehicle's weight. They do not determine ride height. Springs do those jobs. The shock absorber's only job is to control how fast the spring moves. Without shock absorbers, every bump would cause the spring to oscillate — compress, then extend, then compress again, over and over until the energy dissipated naturally. The vehicle would bounce uncontrollably after every bump.

Inside the shock absorber is a piston attached to the rod that moves through an oil-filled tube. As the suspension moves upward, the piston pushes through the hydraulic fluid. Small valves in the piston restrict the flow of fluid from one side of the piston to the other. This restriction creates resistance to movement — damping. The faster the suspension tries to move, the more resistance the shock provides. The suspension moves as quickly as it needs to for normal road use but is prevented from bouncing freely.

A shock absorber works in both directions. Compression — as the wheel moves upward over a bump, the shock compresses and provides resistance to prevent the wheel from slamming into the bump stop. Rebound — as the spring pushes the wheel back down after a bump, the shock provides resistance in the extending direction to prevent the wheel from bouncing back down too fast. Most shock absorbers are valved to provide more resistance in rebound than compression, which is why a failed shock shows its worst effects in rebound — the vehicle continues to bounce after a bump.

Nose-diving under braking. Body roll during cornering more than expected. The front of the vehicle continuing to bounce after hitting a bump. Cupping wear on tires — a wavy wear pattern on the tire tread surface caused by the tire bouncing against the road. Fluid leaking down the outside of the shock body. Any of these indicate worn shock absorbers. Inspecting the actual damping function requires a drive on rough pavement — the bounce test has limited diagnostic value for modern hydraulic shocks.