Caster is the forward or rearward tilting of the wheel axis from the verticle. The center line is an imaginary line that passes through the upper mount and the lower ball joint. A rearward tilt at the top is positive (+) and a forward tilt is negative (-). Zero caster indicates that the strut is directly above the ball joint. Caster influences the directional control of the steering but does not affect the tire wear.

Weak springs or overloading a vehicle will affect caster. Caster affects the vehicle's directional stability and steering effort. The caster angle is calculated to deliver the best in the following:

Caster, like camber, is measured in degrees. The caster specification, along with the Steering Axis Inclination (SAI), is used to give good directional stability and reduce steering effort. If one front wheel has more positive caster than the other, that wheel will pull toward the center of the vehicle. This condition will cause the vehicle to move or lead toward the side with the least amount of positive caster. Caster is not adjustable.