The included angle formed with plumb line as the steering knuckle kingpin axis or hypothetical kingpin
axis tilts backward within longitudinal plane is known as kingpin caster angle, it affects the vehicle driving stability and automatic returning capability. Kingpin positive caster angle: when observing from side of the vehicle, kingpin axis tilts backward within longitudinal plane.
Kingpin negative caster angle: when observing from side of the vehicle, kingpin axis tilts forward within longitudinal plane.
(1)After making a turn, automatic returning capability is insufficient;
(2)Vehicle is unstable under high-speed driving.
Consequence: vehicle deviates off track.
Example: the kingpin positive caster angle of left front wheel is set as 0.3°, that of right front wheel is set as 0.8-0.3°, in such case, the vehicle would deviate toward left.