Uneven tyre wear: what the pattern tells you

Look across the tread, not just at it

Most people check a tyre by glancing at the middle of the tread from the side of the car. The useful information is across the width. Turn the steering to full lock and look at the front tyres from the front, running a hand across the tread from the outside edge to the inside one.

The inside edge matters most, because it is the part you cannot see without doing that, and it is the edge where alignment problems tend to show first.

Both edges worn, centre fine

That is the classic sign of a tyre that has spent its life under pressure. With too little air the tyre sags, the middle of the tread lifts slightly, and the shoulders carry the load.

Under-inflation also makes the tyre run hotter and the steering feel heavier, and it costs fuel. The right pressure is on the placard inside the driver's door opening or the fuel flap, not on the tyre sidewall, and it should be checked with the tyres cold.

Centre worn, edges fine

The opposite. Too much pressure makes the tread crown, so the middle does all the work. It is less common than under-inflation, and it usually comes from someone topping up to the maximum figure printed on the sidewall rather than the figure on the placard.

One edge worn more than the other

This is the pattern that sends people to an alignment, and often rightly. If the wheel is leaning in or out (camber), or pointing slightly in or out (toe), one edge of the tread is scrubbed along the road every metre the car travels.

But alignment is only half the question. A worn control arm bush, a tired ball joint or a sagging spring lets the geometry move under load even when it measures correctly on the machine. Aligning a car with worn suspension parts gives you good numbers for a few weeks. That is why the suspension is checked before the alignment is set.

Feathered tread

Run your hand across the tread one way and then the other. If it feels smooth in one direction and sharp in the other, like the teeth of a saw, the ribs of the tread are being dragged sideways.

That is a toe problem almost every time, and toe is the setting most easily knocked out by a kerb or a pothole.

Cupping and patches

Scalloped dips around the tyre, or patches of wear at intervals, mean the tyre has been bouncing rather than rolling. Each time it comes down it scuffs a patch.

The usual cause is shock absorbers that no longer control the wheel. An out of balance wheel or a bent rim can do it too. You will often hear it before you see it, as a rhythmic drone that changes with speed.

How low is too low

Every tyre has tread wear indicators, small raised bars moulded into the bottom of the grooves. They sit at 1.5 millimetres, the legal minimum in Victoria. When the tread is level with them anywhere across the tyre, it is finished.

Worn unevenly, a tyre can reach that limit on one edge while the rest looks healthy. It is one of the most common reasons a car is held up at a roadworthy inspection.