A tire can tell you a lot about your vehicle. Here are the 10 most common wear patterns and what causes them.
1. Over-Inflation Wear
Wear in the center of the tread pattern indicates inflation pressures are too high. Too much pressure can cause the contact patch to shrink and the center of the tire to carry all of the load.
2. Under-Inflation Wear
Wear on the edges of a tire typically indicate inflation pressures are too low. When a tire is underinflated, the contact patch grows and the load is carried by the outside edges of the contact patch.
Scuffing detected by stroking your fingertips across the edge of each tread bar or tread block indicates excessive positive or negative toe angle. A feather edge on the inside of the tread bar indicates excess toe-in, while a feather edge on the outside of the tread bar indicates toe-out.
Cupped or scalloped dips appearing around the surface of the tread could indicate loose, worn or bent suspension parts. Worn shock absorbers or unbalanced tires can also cause cupping, but the cupping would typically be more indicative of a concentric pattern. Shocks and struts are the most likely culprit because they provide damping force to control tire movement. When the tires move excessively, the scalloped pattern can appear. A lack of rotation can cause this condition.
5. Outer Edge Wear
Wear on the outer edge of a tire is rare these days, but it does happen. Positive camber, caster and toe can lead to wear on the outer edge. If you see edge wear on one side, check the thrust and setback. But, it should be noted, the leading cause of outer edge wear on modern vehicles is over-enthusiastic cornering.
6. Inner Edge Wear – Bushings
Inner edge wear on tires is the most common problem most technicians see. The angles causing this type of wear are typically negative toe and camber. Ozone, extreme temperatures and other atmospheric issues tend to destroy rubber bushings and cause the alignment angles to change. Some vehicles have hydraulic bushings on the rear lower control arms. Some bushings will leak when they fail. When a bushing in the rear fails, the extra movement causes the wheels to toe out and the camber to go negative.
7. Inner Edge Wear – Springs
As a suspension compresses and rebounds, the alignment angles change. Engineers tune alignment angles for a specific ride height to maximize handling and tire wear. If a spring can no longer support the vehicle, the alignment angles will suffer. Most engineers tune the suspension to toe out when the rear suspension compresses. This increases vehicle stability. But, it also causes the inner edge of the tire to wear. Springs are made of metal that is heat-treated, but can still fatigue. This includes leaf, coil and torsion bar springs. If you see a vehicle that needs considerable adjustments for camber on both wheels of the same axle, inspect the springs.
8. Inner Edge Wear – Loads
Loads in the rear of the vehicle will cause changes to toe, caster and camber in the front (and possibly the rear). The camber and caster will become positive in the front, and if the vehicle has an independent rear suspension, the camber will become negative and it will be toed out. This could lead to outside edge wear in the front and inside edge wear in the rear.
9. Flat Spot Wear
A flat spot on the tire, or brake skid wear, occurs when a hard braking situation leads to a skid. The tread hitting the road during the skid is rubbed away from the friction and results in a smooth, flat area. This wear often occurs when brakes lock up, so take a look at the brakes. A flat spot can also be apparent when a car sits for a long time or sat in a corrosive liquid like gasoline or antifreeze.
10. Sidewall Bubble
While technically not a wear pattern, a sidewall bubble is still an issue that indicates a problem with your tire. When a tire hits a pothole or a curb, sometimes instead of blowing, the tire will form a bubble or bulge on the sidewall. The impact damages the tire’s inner liner and creates a small hole or tear. This hurts the strength of the sidewall plies and could cause a blowout.
Adapted from an article in Brake & Front End.