Wheel Alignment
The Angles
Camber tilts the tire top in or out; too much negative camber wears the inner shoulder. Caster is the steering axis tilt and provides directional stability and returnability - it does not wear tires but causes a pull toward the side with less positive caster. Toe is the difference in distance between the front and rear of the tires; incorrect toe causes feathered tread wear and is the largest single tire-wear angle. Thrust angle is the direction the rear axle points relative to the vehicle centerline; if it is off, the steering wheel sits crooked going straight and the vehicle dog-tracks. SAI and included angle help identify a bent strut, knuckle, or spindle when camber cannot be brought into spec.
Pre-Alignment Inspection
Never align a worn front end. Check tire pressures and sizes, ride height, ball joints, tie rod ends, wheel bearings, and steering gear free play. Set pressures and center the steering wheel before reading. Many vehicles require a steering angle sensor reset and, on some, a ride height calibration afterward.
Traps
Confusing cross-camber with cross-caster as the cause of a pull; assuming a crooked steering wheel is toe when it may be thrust angle; and aligning a vehicle with a bent component, which yields a perfect printout and a poor-driving car.
Rule of Thumb
Camber wears, caster pulls, toe feathers. If a car drifts right, compare cross-caster - it pulls toward the side with less positive caster.