FRONT POSITION TIRE WEAR RWD. VEHICLES (ROTATION)

MODELS: ALL LIGHT DUTY TRUCKS

Some rear wheel drive vehicles may exhibit premature tire wear on the front wheel positions. The wear usually starts on the outer tread row and may progress across the full tread. This wear also usually appears as a heel and toe (high and low) wear pattern on individual tread blocks, which can eventually lead to tire noise and/or tire roughness. Small amounts of heel/toe wear on the outer tread are considered normal. This wear is characteristic of new tires at full tread depth on free-rolling axles. Turning and cornering exaggerates front tire wear. Routine tire rotation at 7,500 miles using the modified "X" method as shown in the Owners Manual will minimize the wear. Such tires can be expected to give optimum performance for their full intended life. If this type of wear becomes excessive and/or results in a customer inquiry, the following procedure should be followed:

1. Rotate tires using the modified "X" pattern shown in Figure No. 1. This allows the front tires to rotate in the opposite direction on the rear of the vehicle, which will tend to even out any irregular wear quicker. It also allows all four tires to eventually run on all four positions. Tire noise may continue after rotation, but should gradually lessen after a few thousand miles.

2. Measure front alignment. The single most contributing cause of premature tire wear, except for abusive driving, is excessive toe. For best tire wear, reset toe as close to zero as the specification allows. In most cases, this will be .1 degrees total toe or less. Camber and caster should also be set to specification if necessary.

3. Talk to the customer about his/her tires. Explain that some amount of shoulder wear on front tires is normal and will even out with regular tire rotation. Explain that front tire shoulder wear is also exaggerated by hard cornering. Stress the importance of proper inflation pressure and alignment.

4. If the wear has advanced far enough, tire replacement may become necessary. When installing new tires, match the fire's high point mark* to the wheel's valve and then balance. Also, alignment must be reset as specified in Step 2 above and the customer instructed to follow the modified "X" rotation schedule at 7,500 miles.

* Usually marked with a yellow/green dot on TPC grade tires.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.