There’s more to wheel alignment than following the prompts that appear on a computerized alignment machine. While today’s very helpful wheel alignment systems make it easier and faster to achieve “factory” alignment, it’s important to gain a basic understanding of the terms and geometry involved in wheel angles and the results of angle adjustment.
Types of wheel alignment
The “original” approach of measuring and diagnosing vehicle wheel alignment is referred to as centerline two-wheel alignment, which basically allowed you to only measure (and adjust) front or steering axle wheel positions. This now-outdated method does not factor-in the rear wheel positions and isn’t effective, because it ignores the thrust direction of the rear axle.
The current accepted approach considers the actual location and direction of the rear wheels (even if the rear wheel angles are not designed to be adjustable). This method allows you to include and measure the rear axle thrust line/thrust angle. As a result, this allows you to adjust the front wheel angles relative to the rear wheel angles, regardless of geometric centerline. In the case of a vehicle that does not feature adjustment of the rear wheel angles, this allows us to perform a “four-wheel thrust
If the specific vehicle at hand features an independent rear wheel toe adjustment, we can achieve optimum wheel alignment using the total four-wheel alignment approach, by referring to and adjusting the vehicle thrust angle to as close to zero as possible.
If the vehicle’s rear axle thrust angle is “off zero,” this can result in “dog-tracking” (where the vehicle body appears cocked/crooked relative to direction of vehicle travel), which in turn can contribute to increased tire wear and unequal left/right turning. If the rear wheel angles are adjustable, this allows us to perform a “total four-wheel” alignment.