Tyres and the MOT: Tread Depth, Spare and Sidewall Rules

What the MOT Checks on Your Tyres

The MOT checks that your tyres are legal, safe and correctly fitted. The headline figure is tread depth, which must be at least 1.6mm across the central three quarters of the tyre and all the way around. Anything below this fails. Tyres are one of the most common reasons cars fail their test.

Beyond tread, the tester looks at the condition of each tyre for cuts, lumps and bulges then checks that the size and type are correct for the car. The spare wheel is not part of the test, though it is still worth keeping in good order. Our guide on What an MOT Checks lists all the areas a tester inspects.

The good news is that most tyre faults are easy to spot yourself. A quick look at the tread and sidewalls the day before your test can catch a problem in time, turning a likely fail into a straightforward pass.

What Fails an MOT on Tyres

Several tyre faults will fail the test. Knowing them makes your own pre test check much more useful. The table below sets out the common ones.

The tread rule is the one most people know, though sidewall damage catches out just as many. A bulge in the sidewall is a serious safety risk and an automatic fail. Our guide on Top Reasons Cars Fail MOT covers the other top failure areas alongside tyres.

Understanding the 1.6mm Rule

The 1.6mm minimum applies across the central three quarters of the tyre and around its whole circumference, not just at one point. This means a tyre can look fine on one part and still fail if it is worn below the limit elsewhere, so it is worth checking around the whole tyre.

A simple way to check is the twenty pence test. Place a twenty pence coin in the main tread grooves. If the outer band of the coin is hidden the tread is likely above the limit. If you can see the band, the tyre is close to or below 1.6mm and should be checked properly. Many drivers replace tyres a little before the limit for extra safety and grip in the wet.

Is the Spare Wheel Tested?

The spare wheel and tyre are not checked during an MOT. The test only covers the tyres actually fitted to the car, so a worn or flat spare will not cause a failure. This surprises some drivers who assume everything on the car is inspected.

Even so, a spare is only useful if it is in good condition when you need it. It is worth checking your spare from time to time or knowing how your tyre repair kit works if the car has one instead. It is a safety point rather than an MOT one, though a sensible habit all the same.

Why the Right Tyre Matters

The MOT also checks that your tyres are the correct size and type for the car and are matched properly. Fitting a tyre of the wrong size or mixing radial and cross ply tyres on the same axle is a fail. This is easy to get wrong if tyres are replaced one at a time or bought purely on price, so it is worth checking the markings match the maker's recommendation.

Beyond passing the test, the right tyre is central to how the car handles and stops. Tyres are the only part of the car in contact with the road, so their condition affects braking, grip and safety in the wet more than almost anything else. Our guide on Brakes and the MOT explains how tyres and brakes work together for safe stopping.

Keep Your Tyres MOT Ready

This guide is part of our full MOT Guides hub, where the testing, cost and rules articles sit together so you can move to the exact detail you need next. When it is time to book, our team offers full MOT testing and repairs from our centre in Ely. You may also find it useful to read Top Reasons Cars Fail MOT, Brakes and the MOT and What an MOT Checks.

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