Alignment explained
Toe, camber and caster: move the sliders and watch the wheels.
Alignment is the set of angles each wheel sits at against the car and the road. Three do most of the work. They are small, often less than a degree, and they decide how the car tracks and how its tires wear.
Try it
Each wheel turns on its steering axis, the upright beside it, and the line on the road shows where it points. Drawn larger than real so a real setting shows; it opens on a typical road car.
Camber
- What it is
- The lean of the wheel seen from the front of the car. When the top of the tire leans in toward the car, that is negative camber; leaning out is positive.
- How it is measured
- In degrees from vertical. Most road cars sit between zero and about −1.5°, often with a little more at the rear than the front.
- What it does
- In a corner the body rolls and the outside tire leans with it. A little negative camber offsets that and keeps the tread flat on the road, which is grip. Too much carries the car on the inner shoulder in a straight line: that edge wears first and braking grip drops slightly. Positive camber is rare on modern cars and wears the outer edge.
- When it is off
- One shoulder of the tire worn and the rest of the tread fine: the inner edge with too much negative camber, the outer edge with positive. A car with more positive camber on one side pulls toward that side.
Toe
- What it is
- The direction the wheels point seen from above. When the fronts of a pair point slightly toward each other, that is toe-in; when they point apart, toe-out.
- How it is measured
- As an angle per wheel, in degrees or minutes, or as the difference between the distance across the fronts of the tires and across the backs (A and B), in millimeters or fractions of an inch. Total toe is both sides added together. Road cars sit close to zero.
- What it does
- Toe wears tires faster than any other angle, because a wheel that does not point where the car is going is dragged a little sideways every mile. Toe-in steadies the car in a straight line; toe-out sharpens turn-in but lets it wander.
- When it is off
- A feathered edge on the tread that feels smooth one way and sharp the other when you run a hand across it. Toe-out wears the inner edges, toe-in the outer. A steering wheel that sits off center when the car drives straight usually means the toe was set without centring it.
Caster
- What it is
- The lean of the steering axis seen from the side. The axis is the line the wheel turns about, through the top strut mount or upper ball joint and the lower ball joint. When the top leans back toward the driver, that is positive caster; nearly every car has it.
- How it is measured
- In degrees from vertical. Modern cars run several degrees positive, commonly 4° to 7°.
- What it does
- The axis meets the road ahead of the tire, so the tire trails behind it the way a shopping cart wheel trails its pivot. That gives straight-line stability, steering that returns to center and most of the feel through the wheel. More caster makes the steering heavier and leans the outside wheel in as you turn. On its own it does little to tire wear.
- When it is off
- A pull toward the side with less caster when the two sides differ, or steering that feels light and slow to come back to center. On many cars caster is fixed by the suspension, so a change usually means a bent part or a worn bushing.
Also worth knowing
- Thrust angle
- The direction the rear wheels point compared with the centerline of the car. If they are not square to the body, the car drives very slightly sideways and the steering wheel sits off center to hold it straight. A four-wheel alignment sets the rear first and then sets the front to match it.
- Lowered and track cars
- Lowering a car moves its suspension into a different part of its travel, and on most cars the wheel gains negative camber as it rises, so a lowered car sits with more. Track cars run more on purpose, often 2° to 3° or beyond at the front, because hard cornering leans the tire further and the extra keeps the tread flat when it matters. The cost on the street is inner-edge wear, which is why those cars keep toe close to zero: negative camber and toe-out together wear the inner edge fastest.
- When to have it checked
- After new tires, after suspension or steering parts, after lowering the car, and after a hard hit on a curb or pothole. Also whenever the steering wheel is off center or a tire wears on one edge.
General guidance, not your car's numbers. The alignment spec is in the owner's manual or on the shop's alignment sheet, which lists each angle before and after. This explainer is from Martyr's tips.
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