Caster is the tilting of the upper most point of the steering axis either forward or backward from the vertical (when viewed from the side of the vehicle). 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 designed 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.