Self-levelling Suspension

It is often fitted to the rear axle. It uses air or hydraulics. It keeps headlights aimed correctly. Older systems used hydropneumatic spheres filled with gas and fluid, famous on some French cars; modern ones mainly use air springs at the rear axle. Vans, estates and cars that often tow benefit most. A system that does not level after loading can affect headlight aim and braking.

Sensors detect height and pump air or fluid.

Leaks cause the rear to sag. Faults may show warnings.