Diagnosis and testing. Service procedures

Tire wear patterns

Under inflation will cause wear on the shoulders of tire. Over inflation will cause wear at the center of tire.

Excessive camber causes the tire to run at an angle to the road. One side of tread is then worn more than the other (Fig. 5).

Excessive toe-in or toe-out causes wear on the tread edges and a feathered effect across the tread (Fig. 5).

Fig. 4 Tread Wear Indicators

1 - TREAD ACCEPTABLE

2 - TREAD UNACCEPTABLE

3 - WEAR INDICATOR

Fig. 5 Tire Wear Patterns

Tire noise or vibration

Radial-ply tires are sensitive to force impulses caused by improper mounting, vibration, wheel defects, or possibly tire imbalance.

To find out if tires are causing the noise or vibration, drive the vehicle over a smooth road at varying speeds. Note the noise level during acceleration and deceleration. The engine, differential and exhaust noises will change as speed varies, while the tire noise will usually remain constant.

Rotation

Tires on the front and rear operate at different loads and perform different steering, driving, and braking functions. For these reasons they wear at unequal rates and tend to develop irregular wear patterns. These effects can be reduced by rotating the tires at regular intervals. The benefits of tire rotation are:

• Increase tread life
• Maintain traction levels
• A smooth, quiet ride

The suggested method of tire rotation is (Fig. 6).

Other rotation methods can be used, but they will not provide all the tire longevity benefits.

Match mounting

Wheels and tires are match mounted at the factory.

This means that the high spot of the tire is matched to the low spot on the wheel rim. Each are marked with a bright colored temporary label on the outboard surface for alignment. The wheel is also marked permanently on the inside of the rim in the tire well. This permanent mark may be a paint dot or line, a permanent label or a stamped impression such as an X. An optional location mark is a small spherical indentation on the vertical face of the outboard flange on some non styled base steel wheels.

The tire must be removed to locate the permanent mark on the inside of the wheel.

Before dismounting a tire from its wheel, a reference mark should be placed on the tire at the valve stem location. This reference will ensure that it is remounted in the original position on the wheel.

(1) Remove the tire and wheel assembly from the vehicle and mount on a service dynamic balance machine.

(2) Measure the total runout on the center of the tire tread rib with a dial indicator. Record the indicator reading. Mark the tire to indicate the high spot.

Place a mark on the tire at the valve stem location (Fig. 7).

Fig. 6 Tire Rotation Pattern

Fig. 7 First Measurement On Tire

1 - REFERENCE MARK

2 - 1ST MEASUREMENT HIGH SPOT MARK TIRE AND RIM

3 - WHEEL

4 - VALVE STEM

(3) Break down the tire and remount it 180 degrees on the rim (Fig. 8).

Fig. 8 Remount Tire 180 Degrees

1 - VALVE STEM

2 - REFERENCE MARK

(4) Measure the total indicator runout again. Mark the tire to indicate the high spot.

(5) If runout is still excessive, the following procedures must be done.

• If the high spot is within 101.6 mm (4.0 in.) of the first spot and is still excessive, replace the tire.
• If the high spot is within 101.6 mm (4.0 in.) of the first spot on the wheel, the wheel may be out of specifications. Refer to Wheel and Tire Runout.
• If the high spot is NOT within 101.6 mm (4.0 in.) of either high spot, draw an arrow on the tread from second high spot to first. Break down the tire and remount it 90 degrees on rim in that direction (Fig. 9). This procedure will normally reduce the runout to an acceptable amount, if not replace the rim.

Repairing leaks

For proper repairing, a radial tire must be removed from the wheel. Repairs should only be made if the defect, or puncture, is in the tread area (Fig. 10). The tire should be replaced if the puncture is located in the sidewall.

Deflate tire completely before removing the tire from the wheel. Use lubrication such as a mild soap solution when dismounting or mounting tire. Use tools free of burrs or sharp edges which could damage the tire or wheel rim.

Before mounting tire on wheel, make sure all rust is removed from the rim bead and repaint if necessary.

Fig. 9 Remount Tire 90 Degrees In Direction of Arrow

1 - 2ND HIGH SPOT ON TIRE

2 - 1ST HIGH SPOT ON TIRE

Install wheel on vehicle, and tighten to proper torque specification.