Caster

Caster is the forward or rearward tilting of the wheel axis (the center line is an imaginary line that passes through the upper mount and the lower ball joint) from vertical. A rearward tilt (at the top) is positive (+) and a forward tilt is negative (-). Zero caster indicates that the start is directly above the ball joint. Caster influences directional control of the steering but does not affect 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 steering effort, normal wheel-returning forces and wheel-pulling sensitivity.

Caster, like camber, is measured in degrees. The caster specification, along with 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, it will cause that wheel to 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.