Worn tyres are one of the most common reasons cars fail the MOT – and one of the most expensive mistakes if the police stop you. This guide explains the UK tyre law: the legal minimum tread depth, the penalties, how to check your tyres in a minute and when you should replace them, long before they become illegal.

The legal minimum tread depth

For cars, light vans and light trailers up to 3,500 kg, the legal minimum tread depth in the UK is 1.6 mm. It must be met across a continuous band in the central three-quarters of the tread and around the entire circumference of the tyre.

The law also covers the condition of the tyre. A tyre can be illegal even with enough tread if it has:

  • cuts longer than a certain size or deep enough to reach the cords,
  • bulges, lumps or tears,
  • exposed cords,
  • the wrong type or size for the vehicle, or incorrect inflation for its use.

Penalties for illegal tyres

Driving with an illegal tyre can mean a fine of up to £2,500 and three penalty points per tyre. Because the penalty applies to each tyre, a car with four worn tyres could in theory lead to a combined fine of up to £10,000 and 12 points – enough for a driving ban. Illegal tyres can also affect an insurance claim after an accident.

How to check your tread depth

The 20p test

Insert a 20p coin into the main grooves of the tread. If you can see the outer band of the coin, the tread may be close to or below the legal limit – have it checked by a professional. Repeat the test at several points around the tyre.

Tread wear indicators

Most tyres have small raised bars in the bottom of the main grooves. When the tread is level with these bars, the tyre is at the legal limit.

A tread depth gauge

A cheap gauge gives an exact reading in millimetres and is the most reliable home method.

Why 1.6 mm is not enough

The legal limit is a minimum, not a recommendation. As tread wears, the tyre’s ability to clear water drops sharply, and stopping distances on wet roads increase. Many tyre experts recommend replacing tyres at around 3 mm. In winter, deeper tread matters even more – read are winter tyres worth it in the UK?

Tyre age

Rubber hardens with age even if the car is rarely used. The four-digit DOT code on the sidewall shows when the tyre was made – “4122” means week 41 of 2022. Old tyres may show cracking on the sidewalls; have them inspected.

Tyres and the MOT

At the MOT the tester checks tread depth, condition, size and type. Tyres below 1.6 mm or with serious damage mean a fail. Checking them a few days before the test can save you a re-test. See how much an MOT costs and our inspection checklist.

Uneven wear? Check your alignment

If one edge of a tyre is wearing faster than the rest, the cause is often wheel alignment. Correcting it protects your new tyres – read wheel alignment: when you need it.

Find a tyre shop near you

Kardet lists tyre shops and garages across Europe – see the tyre change category or send a free request with your tyre size.