Category 1
Process of placing a vehicle’s wheels in the correct relationship to the vehicle and the road. Alignment is accomplished by ensuring various steering and suspension system components are properly positioned in relation to each other and the vehicle.
Wheel alignment
Process in which pulling devices are used to bend the frame into position necessary to achieve alignment. Also referred to as frame straightening.
Frame pulling
Alignment procedure in which only the front wheels are adjusted. Two-wheel alignment is performed on many rear-wheel drive vehicles. Also referred to as two-wheel alignment.
Front-wheel alignment
An imaginary line down the center of the vehicle. A perfect thrust line is at a 90° angle to the centerline formed between the rear wheels.
Thrust line
The backward or forward tilt of a wheel away from its centerline when viewed from the side. Measurement in degrees of how much the steering axis varies from an imaginary vertical line.
Caster
Camber adjustment in which the top of the tire is farther away from the vehicle’s centerline than the bottom of the tire when viewed from the front of the vehicle.
Positive Camber
The distance between the fronts of the tires relative to the distance between the backs of the tires. Describes the degree to which the wheels are not parallel to each other.
Toe
The tendency of most roads to slope away from the center. Roads are designed in this manner to assist water runoff.
Road crown
Condition in which the vehicle’s thrust line is not directly on top of its geometric centerline. When this occurs, the vehicle will travel down the road at an angle.
Dog tracking
Metal disc with an off-center hole. Used to adjust an alignment angle. Also referred to as an eccentric cam.
Eccentric
Condition in which the vehicle is lower in the rear, with a corresponding rise in the front suspension. Also referred to as sit down.
Squat