Castor angle

Castor angle is a steering adjustment that can be made for different steering settings in automobiles. The adjustment is done by setting the degree of the pivot points of the steering wheel to a positive or negative degree. 

To understand castor angle, it is best to look at a steered wheel of a vehicle side on. Now, draw an imaginary axis through the steering axis of the wheel of the vehicle. If you tilt the imaginary axis towards the back of the car then you get a positive castor angle and if you tilt the imaginary axis to the front of the car then you get negative castor angle. 

Positive castor improves directional stability and makes the car track straight and true when no steering input is given to the steering wheel. Ideally, a 10-degree positive castor is allowed on regular road cars. But positive castor reduces feedback from the steered wheels of a car to the steering wheel. 

Racing cars are setup with negative castor to improve weight and feel of the steering and improve camber gain while cornering, however, this setting sacrifices on straight line stability of the steering input. Power steering is usually necessary to overcome the added heaviness of the steering wheel.