Alignment questions are a huge part of the A4, and they mostly come down to two things: which way does the car pull, and how do the tires wear?
Here's what each angle does and the rules that answer most of those questions.
Camber
Camber is how far the top of the tire tilts in or out, looking from the front.
The car pulls toward the side with more positive camber. Too much positive camber wears the outer edge. Too much negative camber wears the inner edge.
Caster
Caster is the tilt of the steering axis, looking from the side. Positive caster gives the car stability and makes the steering come back to center.
The car pulls toward the side with less positive caster. If caster is low on both sides but equal, the car won't pull, but it'll wander and the steering won't return well.
Toe
Toe is whether the front of the tires point in or out. Toe out of spec drags the tire sideways as it rolls, which feathers the tread.
- Too much toe-in: feathered wear on the outer edges
- Too much toe-out: feathered wear on the inner edges
Thrust angle and an off-center wheel
Thrust angle is the direction the rear wheels are pushing the car, which is half the difference between the two rear toe readings. If the rear is steering the car off the centerline, the driver has to hold the steering wheel off center to go straight.
On a car with adjustable rear toe, the fix is setting rear toe first, then front toe.
When it won't adjust
If you can't get an angle into spec even with the adjusters maxed out, something's bent. On a MacPherson strut car, SAI and included angle help you figure out which part. And after a subframe has been removed, setback way out of spec usually means the subframe went back in out of position.
Cheat sheet
- Pulls toward more positive camber
- Pulls toward less positive caster
- Positive camber wears the outer edge, negative camber the inner edge
- Toe-in feathers the outer edges, toe-out feathers the inner edges
- Off-center steering wheel: check thrust angle, set rear toe first
Common questions
Which way does a car pull with uneven camber?
Toward the side with more positive camber.
Which way does a car pull with uneven caster?
Toward the side with less positive caster.
What causes feathered tire wear?
Toe out of spec. Too much toe-in feathers the outer edges, and too much toe-out feathers the inner edges.
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