Wheel Alignment

positive caster

Backward tilt of the steering knuckle pivot points from the vertical line.

zero camber

zero camber A tire with no tilt or zero camber angle.

toe-in

When the front of the wheels, as seen from above, are closer together than the rear of the wheels.

toe-out

When the rear of the wheels, as seen from above, are closer together than the front of the wheels.

zero scrub radius

A condition in which the camber line intersects the SAI line at the road surface.

negative scrub radius

A condition in which the camber line is inside the steering axis centerline or when they intersect above the road surface.

positive scrub radius

A condition in which the camber line is outside of the SAI line or when they intersect below the road surface.

turning radius

A measure of how small a circle the outside front wheel on a vehicle can turn around when the steering wheel is turned to the limit.

static toe

A setting designed to compensate for slight wear in steering components that may cause the wheels to turn slightly outward or inward while the vehicle is in motion.

negative caster

Forward tilt of the steering knuckle pivot points from the vertical line.

thrust angle

The angle formed between the perpendicular centerline of the rear axle in comparison to the centerline of the vehicle.

steering axis inclination (SAI)

The angle formed by an imaginary line running through the upper and lower steering pivots relative to vertical as viewed from the front.

caster

The angle formed through the wheel pivot points when viewed from the side in comparison to a vertical line through the wheel.

included angle

The angle of camber added or subtracted to the SAI angle. This is the angle of the steering knuckle pivot points in relation to the camber angle of the wheel; also referred to as a diagnostic angle.

Ackermann angle

The angle the steering arms make with the steering axis, projected toward the center of the rear axle.

toe-out on turns

The difference in turning angle of the inside tire (smaller turning radius) in comparison to the outside tire. This angle difference allows the tires to roll through the corner rather than the inside tire dragging; also referred to as Ackermann angle.

scrub radius

The distance between two imaginary lines—the camber line and the SAI line. Or the point where they intersect above or below the surface of the road.

setback

The distance one wheel is set back from the wheel on the opposite side of the axle.

Ackermann principle

The geometric alignment of linkages in a vehicle's steering such that the wheels on the inside of a turn are able to move in a smaller circle radius than the wheels on the outside.

trim height

The height from the ground to a specified part of the vehicle; also known as ride height.

centerline

The imaginary line drawn down the exact center of the vehicle from front to back.

thrust line

The imaginary line drawn perpendicular to the rear axle.

wheel alignment

The practice of aligning the wheels of the vehicle to the centerline of the vehicle and to one another. It ensures that the vehicle will handle correctly and gives best tire wear.

camber

The side-to-side vertical tilt of the wheel. It is viewed from the front of the vehicle and measured in degrees. Negative camber is when the top of the tire is closer to the center of the vehicle than the bottom of the tire.

postive camber

Tilt of the top of the tire is tilted out from the centerline of the vehicle.

negative camber

Tilt of the top of the tire toward the centerline of the vehicle.