How to Adjust the Kingpin Caster Angle?
3 Answers
The kingpin caster angle and camber angle are fixed and cannot be adjusted. If the kingpin inclination angle of the front axle is inaccurate, the only solution is to replace the front axle. Below is a partial introduction to the inclination angle: 1. The acute angle formed by the projection of the kingpin axis of the automobile steering knuckle and the vertical line on a plane perpendicular to the vehicle's longitudinal symmetry plane is called the kingpin inclination angle. 2. Specifically, when viewing the tire from the front or rear of the vehicle, the kingpin axis tilts inward toward the vehicle body, and this angle is referred to as the kingpin inclination angle. When the wheel rotates around the kingpin, the lowest point of the wheel will sink below the road surface. 3. Additionally, the kingpin inclination angle reduces the distance from the intersection point of the kingpin axis and the road surface to the intersection line of the wheel center plane and the ground, thereby reducing the force the driver needs to apply to the steering wheel during turns. However, the kingpin inclination angle should not be too large, as it would accelerate tire wear.
I've driven trucks for half my life, and nothing scares me more on highways than loose steering. If the kingpin inclination angle is off, the steering wheel feels like a kite with a broken string. Last time I was driving that old Jiefang truck, it kept pulling to the right after hitting a pothole. Took it to my regular repair shop where the mechanic performed a wheel alignment. The diagnostic machine showed the angles were incorrect. Adjusting this depends on the suspension type - my truck uses double wishbones, so the mechanic added different thickness shims to the upper control arm while monitoring the computer data. After adjustment, the truck became much more stable, and the steering wheel now self-centers in turns. This isn't something you can eyeball - you need alignment equipment since even half a millimeter difference in shim thickness can cause tire wear. For vehicles with MacPherson struts, you'd need to replace the top bolts with adjustable ones.
Just adjusted the main rear camber angle on a BMW for a customer yesterday. First secured the alignment target plate on the lift, then connected to the computer to check the camber parameter values—BMW factory specification requires 5.8° to 7.2°. The right front wheel was only at 4.1°, no wonder the steering wheel was shaking. Loosened the fixing bolts on the upper control arm of the suspension system, and slowly adjusted the angle using eccentric shims, checking the data every 15° turn. Stopped at 6.3° and took the opportunity to check tire wear. This kind of precision work must be done with a laser alignment tool; randomly wrenching with a spanner would mess up both the toe and camber angles. German cars typically allow a ±0.5° adjustment range—beyond that, it's recommended to replace with adjustable links. After adjustment, a road test is necessary to check straight-line stability.
