Castor
Castor Caster angle is the tilt of the king pin or ball joint centre line from the vertical towards either the front (negative caster) or rear (positive caster) of the vehicle (Fig. 27.15). The weight of automobile having positive castor tends to turn a wheel inward to allow the body to lower. Negative castor causes an outward turning effect. Wheel castor enables the driver to feel the straight ahead position so that he may steer in a straight path. During cornering, a torque must be exerted on the steering wheel to overcome the self centring or castor action, which tends to keep the wheels pointing straight ahead. The castor angle produces a trailing effect and hence gives the directional stability. Incorrect castor can produce difficulties like hand steering, pulling to one side when brakes are applied and shimmy. To understand the action of this steering feature, the operation of a simple furniture castor (Fig. 27.15A) fitted to a trolley may be considered. Force acting on the t