GA-600S
3D Wheel Aligner User Manual
1-3
1. 3. 3 Steering Axle Inclination
Steering Axle Inclination (SAI) is the angle of steering axis and vertical line (vehicle
front view). As show in Figure 1.3. Correct Kingpin Inclination can equalize the loads
applied on bearings so that the life of bearings can be prolonged and the controllability
of steering is improved. Without the inclination, the controllability of the steering may
be affected; further more, the vehicle weight and the ground counterforce may cause
significant stress in the axle and finally damage the axle. Correct inclination of king pin
is also helpful for the vehicle to restore its straight-ahead position after steering.
Kingpin Inclination is determined when the vehicle suspension is designed. It is not
service adjustable.
Figure 1. 3
Figure 1. 4
1. 3. 4 Caster
Caster is the tilting of the kingpin either forwards or backwards from vertical, as viewed
from side of the vehicle. See Figure 1. 4. When the king pin is tilted backwards from the
vertical, caster is positive. When the king pin is tilted forwards, caster is negative.
Caster angle influences the directional stability of the steering. To increase the
tendency of the steering to self-centre, the steering will normally be designed with
positive caster. Normally caster angle of a vehicle is between 1~4 degrees.
