Tyre wear: how to read the tread and what it says about the car

The tread is a notebook the car writes in daily about its own condition. Reading it is free, takes a minute, and tells you about pressures, alignment, dampers, and driving style at once.

Five typical patterns

Both edges worn, centre intact. Under-inflation. The tyre flexes and the shoulders do the work. Plus higher fuel consumption and longer braking distances.

Centre worn, edges intact. Over-inflation. The contact patch shrinks and grip falls.

One edge worn. Alignment — camber or toe. The most expensive pattern, because the tyre cannot be saved and the cause remains.

Cupping — dampers. The wheel bounces and scrubs the tread unevenly; covered in the dampers article.

Feathering across the blocks — toe. The characteristic sign: run your hand across the blocks and it is smooth one way, sharp the other. This is the main cause of a hum people blame on a bearing; covered in the humming article.

Why one-edge wear is urgent

A tyre worn on the inner edge looks fine from outside. It gets noticed when there is no tread left at all, and in the wet it stopped working long before.

So inspect both sides of the tread, and the inner edge on full steering lock.

Rotating the wheels

Why: front and rear tyres wear differently. Rotation evens out the wear and extends the life of the set.

How often — roughly once a season or every few thousand miles; the handbook is more precise.

The rules:

• Directional tyres are moved front to rear on the same side only, never diagonally.
• Asymmetric tyres have an outer face — it must not end up inboard.
• Different sizes across axles — rotation is impossible.
• After rotating, set the pressures to the specification for each axle.

Important: on cars with indirect pressure monitoring a relearn is needed after rotation; covered in the TPMS article.

Age and depth

Depth — the legal minimum is usually below the practical one. In the wet a tyre loses effectiveness long before it.

Age matters more than people expect: rubber ages by years, not miles; covered in the winter tyres article.

Wear indicators — the raised bars in the grooves; tread level with them means minimum.

What diagnostics sees

The four wheel speeds — differing rolling diameters through wear pull the values apart. On four-wheel-drive cars that also loads the transmission.

Pressure monitoring codes — wheel sensors, or the indirect system through ABS.

Steering angle sensor codes — with changed geometry; covered in the calibration article.

In short

• Both edges worn means low pressure; the centre means high.
• One edge means alignment, and the cause survives the new tyre.
• Cupping means dampers, feathering means toe.
• Inspect the inner edge on full lock.
• Directional tyres are never rotated diagonally.

Download the app — wheel speeds and pressure monitoring codes are read with an ELM327 adapter over Bluetooth SPP on Android.