coilover

A coilover combines a damper (shock absorber) with a coil spring wrapped concentrically around its body. Instead of bolting the spring to a separate location on the chassis, the spring sits directly on the damper itself, creating a self-contained suspension unit. This arrangement saves space, reduces unsprung mass, and allows fine adjustment of ride height by changing the spring's position on the damper rod.

Most road-going coilovers use a threaded collar that slides up and down the damper body, compressing the spring to raise the car or releasing it to lower the car. Some designs include adjustable damping as well, letting technicians tune compression and rebound rates independently. High-performance versions often feature separately valved compression and rebound chambers, while budget units may use a simpler velocity-sensitive design. Spring rates typically range from 6 to 12 kg/mm for street applications, with racing setups running much stiffer.

Setup and adjustment

Lowering the car by compressing the spring changes both ride height and the angle of suspension geometry, which affects camber, caster, and roll center. A 1 cm drop in height can alter wheel camber by 0.5 degrees or more depending on suspension design. This geometry shift is why coilover cars often need four-wheel alignment and why lowering too far causes tire wear and handling problems. Spring preload (the initial compression) does not change the car's height unless the collar position changes.

Coilovers became popular in road racing and rallying during the 1970s because they reduced the amount of chassis work needed to adjust suspension geometry. Factory installations appeared on high-end sports cars starting in the 1990s. Aftermarket coilover kits are now standard tuning parts for performance cars, available as basic units with simple adjustment or complex systems with remote damping controls.

Common failures include oil leakage from damper seals, loss of damping feel when internal valving wears, and noise from worn mounting bushings where the coilover attaches to the chassis. Spring sag, where preload relaxes over time, causes the car to sit lower than expected and is nearly impossible to reverse without replacement. The combination of spring and damper in one unit makes diagnosis harder than separate systems: a soft feel could come from worn springs or worn damping, requiring compression testing to distinguish them.