Steering and Suspension Systems
Alignment angles and their wear patterns
Four angles explain most handling and tire-wear questions. Camber is the inward or outward tilt of the wheel viewed from the front; too much camber wears one shoulder of the tire. Caster is the forward or rearward tilt of the steering axis viewed from the side; it provides straight-line stability and steering return but does not normally wear tires - unequal caster causes a pull. Toe is the difference between the front and rear of the tires; incorrect toe is the biggest single cause of rapid tire wear and shows as feather-edging across the tread. Thrust angle is the direction the rear axle points relative to the vehicle centreline; it causes dog-tracking and an off-centre steering wheel.
Also understand SAI and included angle (used to diagnose bent steering components), turning radius or Ackermann (toe-out on turns), and setback. Tire wear is diagnostic: centre wear = overinflation, both edges = underinflation, one edge = camber, cupping or scalloping = worn shocks or balance, flat spots = lockup or balance.
Components: kingpins and bushings, ball joints, tie-rod ends, drag links, leaf springs, air springs with height control valves, shock absorbers, wheel bearings, and wheel/tire runout.
Worked example. The vehicle drives straight but the steering wheel sits off-centre. Correct it at the drag link, or by adjusting both tie rods equally, rather than re-indexing the wheel - the wheel position is a symptom of the toe setting, not the cause.