How to Adjust Unequal Left and Right Kingpin Inclination Angles?
2 Answers
Different suspension designs have varying definition points for the kingpin inclination angle. For MacPherson suspensions, the caster angle is defined by the suspension's top mount (hard point) and the steering knuckle, while for double-wishbone suspensions, it is defined by the spherical universal joints at the upper and lower ends of the steering knuckle. The kingpin inclination angle is the central rotation axis when the tire rotates. Additional information: 1. When viewed from the side of the vehicle, if the kingpin is tilted backward, it is a positive caster angle (positive-caster); if tilted forward, it is a negative caster angle (negative-caster). 2. The kingpin inclination angle primarily affects handling in two ways: first, its impact on the camber angle, and second, steering feedback and straight-line stability. Regarding the camber effect, assuming a positive caster angle, during steering, the inner half-shaft moves downward relative to the road surface, while the outer half-shaft moves upward. Thus, the kingpin can be considered the rotation center of the wheel hub. 3. Different suspension designs require different methods to adjust the kingpin angle. For MacPherson suspensions, adjustments are made by altering the hard point (top mount), whereas for double-wishbone suspensions, shims are added to the upper control arm for adjustment.
A few days ago I encountered this issue while repairing a car. The owner complained about constant vehicle pulling. Excessive difference in left/right kingpin inclination angles is indeed dangerous and requires professional equipment for adjustment. First, use a wheel alignment machine to measure specific data, focusing on potential suspension damage like deformed lower control arms or displaced shock absorber mounts. Depending on the vehicle model, adjustments are typically made using wedge shims at control arm mounting points, while some models require loosening suspension connection bolts for angle correction. Post-adjustment remeasurement is mandatory - the left/right difference must be within 0.5 degrees to pass. Special caution is required regarding spring tension during the process, as improper handling may damage chassis components.
