Alignment - The Importance of Four Wheel Alignment

88chevy27

Number: 89-01-3A

Section: 3A

Date: SEPT., 1988
Subject: THE IMPORTANCE OF FOUR WHEEL ALIGNMENT


Model and Year: 1979-89 ALL CHEVROLET MODELS



TO: ALL CHEVROLET DEALERS

In which direction will the vehicle pictured below travel if the steering wheel is straight ahead?
The vehicle will track to the left because of the directional forces created by the rear wheels and tires. This directional force is called the "thrust angle". The front wheels aim or steer the vehicle but the rear wheels control tracking and assist in directing the car.

What might the driver comment about?

In the illustration, the driver may comment about the steering wheel being off center when going straight down the road. This would be true because of the added input required at the steering wheel to offset the thrust angle force caused by the rear wheels not tracking the front wheels to the geometric center line of the vehicle.
The driver may also comment about unusual tire wear, not precise handling characteristics and even decreased fuel economy.

A four wheel alignment allows the technician to measure the toe of each rear wheel to determine if the rear wheels are tracking the geometric center line of the car. Ideally the geometric center line will be the same as the thrust line. In the example in Figure 1, the thrust line has shifted to the right because the rear wheel toe is not tracking the front wheels. This can occur on both or on one rear wheel.

On some vehicles the rear toe is adjustable; other models may require component straightening or replacement or shims. Once the rear toe is properly adjusted or set, the front wheel toe can be set so all four wheels are tracking the geometric center line of the vehicle. This will provide optimum tire wear, handling and fuel economy characteristics for the vehicle.