Wheel Alignment Theory & Operation - General Information: Adjustments: Caster

1. Caster is tilting of front steering axis either forward or backward from vertical, as viewed from side of vehicle. See Fig 1.
2. When axis is tilted backward from vertical, caster is positive. This creates a trailing action on front wheels. When axis is tilted forward, caster is negative, causing a leading action on front wheels.

Fig 1: Determining Caster Angle