Wheel Alignment Diagnosis, Adjustment, and Repair
Alignment on a transit bus is about camber, caster, toe, thrust angle, and steering axis inclination (SAI), plus included angle and turning angle. Know what each does: camber affects tire wear and directional pull; caster affects straight-line stability and returnability; toe affects tire scrub and is the most wear-sensitive angle; thrust angle describes the rear axle's relationship to the vehicle centerline; SAI and included angle help diagnose bent steering components.
Reading the angles
A pull to one side with correct toe often traces to camber or caster split. Uneven tire wear across the tread suggests camber; feathered edges suggest toe. A crooked steering wheel with correct front toe points to rear thrust angle. SAI that is out of spec on one side but not the other suggests a bent spindle, knuckle, or strut.
Traps
- Adjusting toe before camber and caster - changing camber moves toe.
- Forgetting to center the steering wheel and check thrust angle first.
- Ignoring ride height, tire pressure, and load when taking readings.
Rule of thumb
Set rear thrust angle first, then front camber, then caster, then toe last. Toe is always the final adjustment because every prior adjustment changes it.