Car and truck suspension springs generally fall into three categories: leaf springs, coil springs, and torsion bars. These springs support the vehicle, allowing it to react smoothly to road height differences, bumps, and dynamic vehicle loading, like passengers, cargo, braking, and turning. While springs will continue oscillating until acted on by an outside force, shock absorbers will eventually wear out, which is why shock absorber replacement should be on your radar.

Shock absorbers are pistons filled with hydraulic fluid, connected between the body or frame and control arms or axles. The hydraulic fluid in the shock absorber flows through restrictive valves, exerting resistance to the spring’s oscillations.

Hydraulic damping or shock absorption is important, because too much bounce can be both uncomfortable and dangerous. Worn suspensions often lead to a boat-like ride quality, which can make people queasy, and, more dangerous, lead to abnormal wear patterns and tire noise. Then, if a tire and wheel start bouncing uncontrollably—no damping—the tire can bounce right off the road. In a corner or a high-speed stop, this could lead to a loss of vehicle control.