Are Your Tyres Legal? Tread Depth, the Law and When to Replace (2026)

Tyres are the only part of your car that actually touches the road — and they're also one of the most common reasons cars fail their MOT and one of the easiest things to get caught out on. Before a long summer drive, five minutes checking them is well worth it. Here's the law, the quick tests, and when to replace.

The legal limit: 1.6mm

In the UK, the minimum legal tread depth is 1.6mm, across the central three-quarters of the tyre and all the way around. Drop below that and the tyre is illegal — and the penalties are steep: up to £2,500 and 3 penalty points per tyre. Four bald tyres could, in theory, mean a £10,000 fine and the loss of your licence. Worse, illegal tyres usually invalidate your insurance, leaving you exposed if the worst happens.

But 3mm is the smarter number

Legal isn't the same as safe. Tests consistently show that wet-weather stopping distances increase sharply once tread falls below 3mm — long before you hit the legal limit. That's why many safety bodies recommend replacing at 3mm, especially if you do motorway miles or drive in the rain. Think of 1.6mm as the point you must never go below, and 3mm as the point to start planning.

The 20p test

You don't need a gauge. Take a 20p coin and push it into the main grooves:

• If the outer band of the coin is hidden by the tread, you're likely above the legal limit.
• If you can see the band, your tread may be too low — get the tyre checked.

Do it at a few points around each tyre, and on all four. Uneven wear (more on one edge) can also signal a tracking or pressure problem worth fixing.

Age matters as much as tread

Here's the one people miss: tyres degrade with age, even with plenty of tread. Rubber hardens and cracks over the years, especially with sun exposure — so a low-mileage car with old tyres can be just as risky as a worn one. Many manufacturers advise replacing tyres at around 10 years regardless of wear.

Check the age on the sidewall: look for a four-digit code (the last four of the "DOT" number). "2624", for example, means the 26th week of 2024. If your tyres are pushing a decade, replace them whatever the tread says.

Don't forget pressure

Under-inflated tyres wear faster, use more fuel and are more likely to fail at speed — a real risk on long, hot summer drives. Check pressures when the tyres are cold, using the figures in your handbook or on the door-frame sticker (not the maximum printed on the tyre itself). Include the spare if you have one.

The bottom line

Your tyres are non-negotiable: 1.6mm is the legal floor, 3mm is the safe replace-point, and age can finish a tyre even when tread can't. Run the 20p test, check the dates, and sort your pressures before any big trip. If your MOT is also coming up, tyres are one of the first things the tester looks at — you can check when your MOT is due free with the registration and avoid a surprise fail.