Reading the wear pattern on a tire

Uneven tire wear is a symptom, and the location and shape of the worn tread point toward its likely cause. A tire that wears evenly across its width and around its circumference is usually doing its job. When the tread is worn in the center, along both edges, on one side, in sharp-edged blocks or in repeated dips, the pattern suggests whether the problem lies with inflation, alignment or the suspension.

Look at all four tires, not just one. The front pair and rear pair can differ, and a difference between left and right usually points to something at one corner of the car. Run a hand across the tread as well as looking at it, because some wear is easier to feel than to see. Rotating the tires can even out normal wear, but it does not fix the cause, so the pattern will return on the new positions if the underlying issue remains.

Center wear points to overinflation

When the center of the tread wears faster than the shoulders, the tire is usually running at too high a pressure. An overinflated tire bulges slightly in the middle, so the center carries most of the load and wears away first. The contact patch also becomes smaller, which reduces grip, especially in wet conditions. Check the pressure with a gauge against the placard value, and let air out in small amounts until the reading matches.

Overinflation is often the easiest pattern to correct, because it usually comes down to setting the pressure correctly. If the center wear is severe, though, the tire may already have lost much of its useful tread, and replacement should follow the same guidance as any tire that is worn down. Checking the pressure monthly helps prevent the problem from developing further, since pressure changes with temperature and center wear builds up gradually over the life of the tire.

Edge wear on both sides points to underinflation

When both shoulders, the outer edges of the tread, wear faster than the center, the tire has most likely been driven underinflated. The tire sags, so the edges take more of the load and the sidewalls flex with every turn of the wheel. Underinflated tires also run hot, which speeds wear and can contribute to tread separation at high speed.

Edge wear is a pressure problem first, so check the placard value and inflate the tires to it before assuming the suspension is at fault. If the edges keep wearing after the tires are held at the correct pressure, a heavy load or a steady loss of air may be involved. A tire shop can inspect the tire for a slow leak and check the sidewalls for damage that would also explain the pattern.

One-sided wear points to alignment

Wear on only one shoulder, either the inner or the outer edge on one side of the tire, usually points to camber, the angle at which the tire sits when viewed from the front. Positive camber, where the top of the tire leans outward, wears the outer shoulder. Negative camber, where the top leans inward, wears the inner shoulder. Camber can change when suspension parts wear, when a car hits a pothole or curb hard, or when an earlier repair altered the geometry.

Because one-sided wear comes from the geometry of the car, rotating the tires or inflating them correctly will not solve it. A technician should measure camber and toe with an alignment machine and check the suspension components, including ball joints, control arm bushings and tie rods, for play. Once the geometry is restored, consider replacing badly worn tires, so the new ones do not inherit the uneven pattern.

Feathering and toe

Feathering is a pattern where each tread rib has one edge worn sharper than the other, which you can feel by running a hand across the tread in one direction and then the other. Toe misalignment, where the front wheels point slightly inward or outward relative to each other, is the usual cause. The tire scrubs sideways as it rolls and gradually shaves the tread into angled blocks. On a car with badly set toe, this wear can develop quickly, sometimes faster than owners expect.

A feathered tire should go to an alignment check, not just a rotation. A toe reading outside specification is typically corrected at an alignment shop, and the technician may also check the tie rods and steering components for looseness. Feathering on both front tires usually points to toe. A difference between the two sides suggests that a part at that corner should be checked.

Cupping and what to do next

Cupping, sometimes called scalloping, appears as a series of dips or scoops spaced around the tire. It often repeats at the same interval on each rotation and can produce a hum or growl that changes with speed. Worn shock absorbers or struts are a common cause, because the tire briefly loses contact with the road as it bounces. Unbalanced tires and loose or worn suspension components can also produce the pattern.

The practical order is to start with the inexpensive checks and then move to the costly ones. Confirm the pressure, have the wheel balance checked, and have the suspension and steering inspected by a technician. Replacing worn shocks or struts often stops further cupping, but the damaged tires will not regain the lost tread, so they may still need replacing. The pattern is most useful when it is brought to a shop together with the symptoms you have noticed while driving, such as a noise, a vibration or a change in steering feel.