What is the difference between a thrust angle alignment and a four-wheel alignment?
During an alignment, two benchmarks are used to determine the relationship between the vehicle and the tires. The first is the vertical reference line: an imaginary line that runs through the center of the tire/wheel assemblies. The second is the centerline: an imaginary line that bisects the vehicle lengthwise. Ideally, the centerline and thrust angle will be the same. The thrust angle and centerline are different, the vehicle will dog track down the road and the steering wheel will be off-center. On vehicles with non-adjustable rear suspension, the thrust angle is fixed based on the position of the rear wheels. In a thrust angle alignment, the front wheels are aligned according to the measured thrust angle. This procedure is used for rear-drive vehicles with a solid axle. For vehicles equipped with adjustable rear wheels, a four-wheel alignment can be performed. During this procedure, the thrust angle is adjusted to zero (center) prior to aligning the front wheels.
