For 1990-2009 cars

Caster is the tilting of the front steering axis (at the top) either forward or backward (3) from the vertical (1). A backward tilt is positive (+) and a forward tilt is negative (-). Caster influences the directional control of the steering but does not affect the tire wear and is adjustable only at the front tires and wheels.

Caster is affected by the vehicle height. Therefore it is important to keep the body at the designated trim height. Overloading of the vehicle, or a weak sagging rear spring will affect the caster. When the rear of the vehicle is lower than the designated trim height, the front suspension moves to a more positive caster. If the rear of the vehicle is higher than the designated trim height, the front suspension moves to a less positive caster. For trim height information, refer to Trim Height Specifications in Suspension General Diagnosis.