Wheel Alignment and Geometry
What the candidate must know
Master the primary angles: camber, caster, toe, thrust angle, steering axis inclination (SAI), and included angle. Know which are adjustable on a given chassis and which are not. Understand toe as the biggest tire-wear angle, camber wear on the inside or outside shoulder, and caster's effect on wander and returnability. Know thrust angle (rear axle alignment relative to the vehicle centerline) and how it causes dog-tracking and a crooked steering wheel. Understand SAI/included angle as a diagnostic for bent spindles or knuckles.
Traps in questions
- Blaming a pull on camber when the real cause is caster split, tire conicity, or a dragging brake.
- Forgetting that toe wear shows as feathered tread across the tire, while camber wear is one-shouldered.
- Misreading thrust angle - it is a rear-axle condition that presents as a front-end symptom.
- Assuming all angles are adjustable; on solid axles, caster and camber often require shims or bending per OEM procedure.
Rule of thumb / worked example
A bus with a straight-ahead steering wheel that is off-center and rear tires wearing on one edge suggests a thrust angle problem. Measure rear toe and thrust angle first; correct the rear axle (shift, shim, or replace worn parts) before touching front toe. Then set front toe last, centering the wheel through the tie rods. Remember the sequence: rear first, then front, toe last.