When inspecting tires, you should look closely at the outer sidewall, tread area, and inner sidewall for bulges, splits, cracks, chunking, cupping, and other abnormal wear or damage. If problems are found before repairing or replacing the tire, determine what caused the failure.

Tire Impact Damage

Tire impact damage or road damage includes tears, punctures, cuts, and other physical injuries. Depending upon the severity of the damage, the tire must either be repaired or replaced.

Tire Wear Patterns

Tire wear patterns can be studied to determine the cause of abnormal tread wear. By inspecting the tread wear, you can determine what parts should be serviced, repaired, or replaced. Common tread wear patterns are as follows (fig. 8-47):

FEATHERING (A) is caused by erratic scrubbing against the surface of the road when the tire is in need of toe-in or toe-out alignment correction.

OVERINFLATION (B) causes fast center line wear in bias and bias belted tires. In this case, the center of the tread has more contact with the road and wears faster than the outer area of the tread.

UNDERINFLATION (C) causes the outer tread areas (shoulders) of the tire to have more contact with the road; therefore, they wear faster than the center area of the tread.

ONE-SIDE WEAR (D) is caused by excessive camber, which means that the tire is leaning too much to the inside or outside. This places all the work on one side of the tire, resulting in excessive wear.

CUPPING (E) is caused by several problems, such as imbalanced wheels. faulty shock absorbers, faulty ball joints. or a combination of these troubles.

Tire Inflation Problems

The correct tire inflation pressure is important to the service life of the tire. Proper inflation is required to ensure that the tread of the tire fully contacts the road surface. This condition allows for even wear across the tread, therefore. resulting in increased tire life and improved handling and safety.

Tire overinflation causes the center area of the tread to wear quickly. The high pressure causes the

Figure 8-47. - Tread wear patterns.

body of the tire to stretch outward, pushing the center of the tread against the road surface. This action lifts the outer edges of the tread OFF the road. An overinflated tire produces a rough or hard ride. It is also more prone to impact damage.

Tire underinflation is a very common and destructive problem. This condition wears the outer edges of the tread (shoulders) because low pressure allows the sidewalls of the tire to flex which builds up