Short answer: the shape of the wear names the cause. Wear on both edges with a healthy center means the tire has been running underinflated. Wear down the center only means overinflated. Wear on one edge only points at camber, which is alignment or a worn suspension component. Sharp edges on one side of each tread block points at toe. A wavy, scalloped surface points at worn suspension or a balance problem. Each of those is a different bill, and you can tell which one you are looking at in about a minute.
Your tires are the cheapest diagnostic instrument on the car. They record what the suspension and alignment have been doing for thousands of miles, and they report faults long before you feel them through the wheel.
How to look, and when
Do it on a level surface with the car parked, and look at all four tires rather than the one you happened to notice.
Run your hand across the tread from one shoulder to the other, in both directions, as well as looking. Some patterns are much easier to feel than to see, particularly feathering, which produces a surface that feels smooth one way and sharp the other.
Also compare tires with each other: front against front, left against right, front against rear. A pattern on one corner points somewhere very different from the same pattern on all four.
Good moments to do this: whenever you check pressures, whenever the tires are rotated, and any time the car has started to feel different.
Wear on both edges, center strip fine
Cause: chronic underinflation.
An underinflated tire bulges so that the shoulders carry more load than the center. The edges do the work and wear accordingly, and the tire also flexes more, runs hotter, and costs you fuel.
This is the cheapest problem on the page to fix and the most consequential to ignore, because underinflation is also the condition most associated with heat-related tire failure. Correct pressure is on the placard in your driver’s door jamb, not the number moulded into the tire sidewall, which is a maximum rather than a specification.
If your tire pressure lamp has been coming on, our guide on why the TPMS light is on when the tires look fine covers why a tire can be well down on pressure and still look normal.
Wear down the center only
Cause: overinflation.
An overinflated tire crowns in the middle, so the center strip carries the load and wears while the shoulders stay comparatively fresh. Grip and ride quality both suffer, and the tire is more vulnerable to impact damage from potholes.
Also cheap to fix, and again the placard is the reference. This one is more common than people expect on vehicles where somebody has inflated to the sidewall maximum.
Wear on one edge only
Cause: camber, meaning the wheel is tilted relative to vertical.
Negative camber tilts the top of the wheel inward and wears the inside edge. Positive camber tilts it outward and wears the outside edge. Either way, one shoulder is carrying load the other is not.
Two underlying reasons. Alignment, which can drift after hitting a curb or a pothole, or after suspension work. Or worn suspension components, where perished bushings, a tired ball joint or a sagging spring let the geometry move.
That distinction matters because an alignment on a car with worn components does not hold. Whether an alignment offer is genuine is covered in our guide on whether you actually need a wheel alignment.
Feathering: sharp on one side of each tread block
Cause: toe, meaning the wheels are pointing very slightly inward or outward relative to each other.
Feathering is the pattern you feel rather than see. Each tread block has a smooth, rounded edge on one side and a sharp, stepped edge on the other. Run your hand across the tread one way and it feels smooth; the other way it catches.
A wheel that is not pointing exactly where the car is travelling scrubs sideways a fraction on every rotation, and that scrubbing shaves each block asymmetrically. Causes are the same as camber: alignment knocked out by impact, worn steering or suspension components, or changes after work was done.
Feathering is the most reliable early warning of a toe problem, and it usually appears well before the car feels wrong to drive.
Cupping or scalloping: a wavy surface
Cause: usually worn suspension, sometimes imbalance.
Cupping looks like a series of dips or scooped-out sections spaced around the tread. It is caused by the tire bouncing rather than staying planted, so it makes contact unevenly as it rotates. Worn shocks or struts are the classic reason, since damping is exactly what keeps the tire on the road. An out-of-balance wheel or a bent wheel can do the same.
Cupping usually announces itself with noise and vibration at speed, and it is the pattern most likely to be mistaken for a failing wheel bearing.
This one is worth acting on rather than monitoring. A tire that is not maintaining consistent contact with the road is a tire that is not braking or steering consistently either.
Patchy or flat-spotted wear
Cause: usually balance, occasionally braking or a driving habit.
Isolated flat areas or irregular patches with no repeating rhythm generally point at wheel balance, and sometimes at a wheel that has been locked briefly under braking or a tire that sat under load without moving for a long period.
If it appears alongside a pull or a vibration under braking, treat the brake symptom as the lead, as covered in our guide on a car that pulls to one side when braking.
What to do with what you found
Pressure patterns, meaning both-edges or center wear: correct the pressures to the placard, then recheck in a few weeks to confirm they are holding. If a tire keeps dropping, it has a leak rather than a habit.
Geometry patterns, meaning one-edge or feathering: book an alignment check, and ask them to inspect the suspension and steering components at the same time. An alignment on worn parts is money spent twice.
Suspension patterns, meaning cupping: have the shocks, struts and bushings inspected. Balance too, but do not assume balance is the whole answer.
In every case, note which corner. “The left front inner edge” is dramatically more useful to a technician than “one of the tires is worn.”
Why new tires do not fix the pattern
This is the part that costs people money twice.
A wear pattern is a symptom. The alignment problem, the worn bushing, the failed shock or the pressure habit that produced it is still there when the new tires go on, and it will produce the same pattern again on the new set.
So the sequence matters: find and fix the cause first, or at minimum have it assessed at the same time the tires are replaced. Fitting new tires to an uncorrected fault is the most reliable way to buy tires twice.
Tread depth is only half the replacement question, incidentally. Age matters independently, and a tire with plenty of tread can still be too old to trust, as covered in our guide on when a good-looking tire is too old to trust. For how tire symptoms sit alongside brake and steering symptoms, our guide to brake, tire and steering warning signs is the pillar for this cluster.
Frequently asked questions
What causes wear on both edges of a tire?
Chronic underinflation. The tire bulges so the shoulders carry more load than the center. Set pressures to the placard in your driver’s door jamb rather than the maximum on the sidewall.
What does wear in the middle of the tread mean?
Overinflation. The tire crowns in the center, so the middle carries the load and wears while the shoulders stay comparatively fresh.
What is tire feathering?
A pattern where each tread block is smooth on one side and sharp on the other, felt more easily than seen. It points at a toe alignment problem, often after an impact or from worn steering and suspension parts.
What causes tire cupping?
Usually worn shocks or struts letting the tire bounce rather than stay planted, sometimes wheel imbalance or a bent wheel. It typically comes with noise and vibration at speed.
Will new tires fix uneven wear?
No. The alignment, suspension or pressure problem that caused the pattern is still there and will reproduce it on the new set. Find the cause first or assess it at the same time.