For 1990-2009 cars

Caster is the tilting of the front steering axis (at the top) either forward or backward from the vertical (1). A backward tilt is positive (+) and a forward tilt is negative (-). Caster influences directional control of the steering, but does not affect tire wear.

Caster is affected by vehicle height, therefore it is important to keep the body at its designed height. Overloading the vehicle or a weak or sagging rear spring will affect the caster. When the rear of the vehicle is lower than its designated trim height, the front suspension moves to a more positive caster. If the rear of the vehicle is higher than its designated trim height, the front suspension moves to a less positive caster.