Castor angle

Castor angle is the angular measure from the vertical of the suspension of a steered wheel in a car or other vehicle, measured in the longitudinal direction.

The pivot points of the steering[?] are angled such that a line drawn through them intersects the road surface alightly ahead of the contact point of the wheel. The purpose of this is to provide a degree of self-centring for the steering - the wheel castors around so as to trail behind the axis of steering. This makes a car easier to drive and improves its straight line stability (tendency to wander). Excessive castor angle will make the steering heavier and less responsive, so performance cars often have only very small castor angles.