Tips & Guides

A tire wearing evenly across its width is doing its job. A tire wearing in one place is telling you something, and the pattern is specific enough to name the cause. Both shoulders means pressure. One shoulder means alignment. A sawtooth edge means toe. Scalloped dips mean the wheel is bouncing.

We also looked at what owners themselves report. Across 5,950 analysed reviews, the thing raised most often isn’t a wear pattern at all. It’s vibration, at double the rate of tread life, and when in a tire’s life it arrives tells you whether wear has anything to do with it.

Reading the pattern

Uneven wear is almost always a symptom rather than a fault in itself. The tire is recording, in rubber, something about how it has been loaded, aimed or supported. Read the pattern and you get the cause, usually without any diagnostic equipment.

Run your hand across the tread, then along it. Look at both edges. Compare the tire to the one on the other side of the same axle. That comparison alone separates a pressure problem, which affects all four, from an alignment problem, which usually doesn’t.

Swipe the table sideways to see every column.

Both shoulders worn

This is underinflation, and it is the most common wear fault there is.

An underinflated tire cannot hold its crown flat against the road. The centre of the contact patch lifts slightly and the load transfers outward onto the shoulders, which then carry more than their share for every mile you drive. The wear follows the load.

It is worth being precise about why, because a version of this article previously blamed compound hardness: a softer centre flexing more than stiffer shoulders. That is not the mechanism, and where tires do use more than one compound it usually runs the other way, with softer shoulders for cornering grip. What drives shoulder wear is contact pressure distribution, which is geometry.

Check pressure cold, against the placard on the driver’s door pillar rather than the number moulded into the sidewall. The sidewall figure is the maximum the casing can hold, not a target.

Centre worn

The same mechanism in reverse. Overinflation bows the crown outward, the centre of the tread takes a disproportionate share of the load, and it wears ahead of the shoulders.

This is worth catching early rather than late. Correcting the pressure stops the pattern getting worse, but it doesn’t put the rubber back. Whether the tire needs replacing depends on how much tread is left in the worn section, not on the pattern itself. Measure it before deciding.

One shoulder worn

When the wear is on one edge of one tire, you are looking at alignment, and specifically at camber.

Camber is how far the wheel leans from vertical, viewed from the front of the car:

• Negative camber means the top of the wheel leans inward, toward the vehicle. It loads the inner shoulder, so that is where the wear appears.
• Positive camber means the top leans outward. It loads the outer shoulder.

A small amount of negative camber is designed in on most vehicles, because it helps the outside tire stay flat during cornering. Wear only becomes a problem when the angle drifts outside specification, usually after a kerb strike, a pothole or a worn suspension bush.

Inner shoulder wear in particular is worth naming plainly: it is an alignment symptom, not a manufacturing defect. A warranty claim on that basis will be declined, and correctly so. Get the alignment measured, fix what the sheet says is out, then judge whether the tire still has usable tread.

Feathering

Run your palm across the tread, from one shoulder to the other. If it feels smooth in one direction and sharp in the other, like the teeth of a saw, that is feathering, and it points at toe.

Toe is whether the wheels point slightly toward each other or away, seen from above. When it is out of specification the tire is dragged sideways a fraction of an inch for every rotation, and each tread block wears at an angle rather than square. Excessive toe-in tends to scrub the outer edges; toe-out tends to scrub the inner ones.

Feathering is easy to miss because it is a texture rather than a shape. The tire can look fine and still be telling you the alignment is out. It is also the one pattern you are most likely to find with your hand before your eye.

Heel and toe

Here each tread block is worn lower at one end than the other, so the tread feels like a row of small ramps when you run a hand along the tire rather than across it.

On a lug-type pattern, a degree of this is normal, and it appears early. An individual block flexes as it enters and leaves the contact patch, and the trailing edge scrubs slightly more. Rotating on schedule redistributes it, which is why the hum that sometimes comes with it often fades after a rotation or two.

It becomes a fault only when it is pronounced, one-sided, or accompanied by other patterns. Then it is usually pointing at the same things cupping does.

Cupping

Cupping, or scalloping, is a series of dips around the circumference of the tire, spaced fairly evenly. It means the tire is not staying in contact with the road consistently. Something is letting it bounce.

The usual causes, in rough order of how often they turn out to be responsible:

• Out-of-balance assembly. A heavy spot makes the tire hop at a specific speed range, and it wears where it lands.
• Worn dampers. A shock that has lost its control lets the wheel oscillate after every bump instead of settling once.
• A bent or damaged wheel. Same effect, different origin.
• Alignment far enough out that the tire is being dragged as well as rolled.

The symptoms usually arrive before the pattern is obvious: a rhythmic hum that rises and falls with speed, vibration that appears in a band rather than getting steadily worse, and sometimes a pull to one side.

Catch it while the dips are shallow and a rotation plus a rebalance can even things out. Once the pattern is established, the tire will keep generating its own vibration regardless of what you fix underneath it.

Cut and chip

Small pieces torn out of the block edges, rather than worn away. Chipping is the fine version, cutting the coarser one.

This is a surface and compound question rather than a mechanical one. Sharp aggregate, rock and gravel load the leading edges of tread blocks hard enough to tear rubber rather than abrade it. Compounds built for cut and chip resistance handle it; road-biased compounds on the same surface do not.

If it appears evenly on all four tires in conditions the tire is sold for, the compound is a fair question to put to the manufacturer. If it appears on the tires that see the roughest use, or after a specific trip, the surface is the more likely answer.

What owners report

Everything above is diagnosis. This is frequency: how often each of these actually comes up when owners write about their tires.

One distinction matters before reading the numbers. Tread life and chunking are wear patterns. Vibration is a symptom, and it sits on both sides of the wear question: an out-of-balance assembly causes cupping, and a cupped tire then generates vibration of its own. It can also have nothing to do with wear, which is the most common case of all.

Two things stand out.

Vibration is reported more than any actual wear pattern. It comes up in 5.2% of reviews against 2.5% for tread life. Wear guides tend to mention balance in passing, inside a paragraph about cupping. For owners it is the headline complaint, whether or not the tread has anything to do with it.

Chunking is rarer than its reputation. At 0.4%, cut and chip is discussed far more than it is experienced, even in a set of reviews dominated by off-road-oriented all-terrain tires. It is real, and it matters when it happens, but it is not a common outcome.

Tread life is worth reading in both columns. It is raised approvingly in 13.4% of reviews and as a complaint in 2.5%, which is roughly five owners pleased with it for every one who isn’t.

When the complaints arrive, and what that tells you