Caster is the tilting of the steering axis either forward or backward, and is measured in degrees. It is adjusted by changing the position of the upper ball joint in relation to the lower ball joint. Caster affects directional stability and steering returnability. If caster is too high, the steering will be heavy and difficult to turn. If caster is too low, the steering will be light and may cause the vehicle to wander. The ideal setting for caster is when the steering wheel is in the straight-ahead position and the vehicle is traveling in a straight line.