Caster is the tilting of the uppermost point of the steering axis either forward or backward from the vertical (viewing from the side of the vehicle). A backward tilt (at the top) is positive (+). A forward tilt (at the top) is negative (-). Caster influences the directional control of the steering. Caster does not affect the tire wear. If one wheel has a more positive caster than the other, this condition will cause the vehicle to move or lead toward the side with the least amount of positive caster.