Caster is the tilting of the front steering axis, either forward or backward from the vertical (1). A backward tilt is positive, and a forward tilt is negative. The wheel will pull toward the center of the vehicle if one wheel has more positive caster than the other. This will cause the vehicle to move or lead toward the side with the least positive caster. Caster influences directional control of the steering, but does not affect tire wear. Weak springs or overloads will affect caster.