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 heat during operation. The center of the tread flexes upward and does NOT touch the surface of the road. Underinflation will cause rapid tread wear, loss of fuel economy, and possibly ply separation (plies tear away from each other).

Uneven tire inflation pressure can cause steering wheel pull. For example, when a vehicle that ha's the left front tire underinflated and the right front tire properly inflated, the vehicle has a tendency to pull to the left. The low air pressure in the left tire has more rolling resistance. This action tends to pull the steering wheel away from the normally inflated tire.