Tyre tread depth and the MOT: the legal limit and how to check

Tyres are the only part of your car that touches the road, so it's no surprise that the MOT checks them closely. Tyre problems are among the most common reasons for an MOT fail, and among the easiest to spot yourself beforehand.

In DVSA's 2023 data, 6.3% of cars failed their MOT on tyres.

The legal tread depth

For cars, the minimum legal tread depth is 1.6mm. That depth must be present:

• across the central three-quarters of the tread width, and
• around the entire circumference of the tyre.

The outer edges can be worn below this without breaking the rule, though uneven wear like that usually points to a tracking or pressure problem.

Most new tyres start with around 7–8mm of tread. Many experts and tyre makers recommend replacing them at 3mm, because braking distances in the wet increase significantly as tread wears down.

How the MOT tests tyres

The tester looks at every tyre fitted to the car. They check:

A dangerous defect means the car can't be driven away until it's fixed. Our guide to MOT defect categories explains what each category means.

How to check your tread depth

The 20p test

Put a 20p coin into the main grooves at several points around each tyre. If the outer band of the coin is hidden, the tread is probably above the legal limit. If you can see the band, the tread may be close to or below it, so get the tyre checked properly.

Tread wear indicators

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

A tread depth gauge

A gauge costs a few pounds and gives an exact reading. Check across the width of the tyre (inner, middle and outer) and at several points around it, because tyres rarely wear evenly.

Other things to look for

Tread isn't the only thing that matters. Before an MOT, walk round the car and check each tyre for:

• cuts, lumps and bulges on the sidewall, which can mean the internal structure is damaged
• cracking, which is common on older tyres or cars that stand still for long periods
• objects such as nails or screws in the tread
• uneven wear, such as one edge much more worn than the other
• the correct pressures, which you'll find in the handbook, inside the fuel flap or on the driver's door frame

If the tyre pressure warning light stays on after you've corrected the pressures, there may be a fault with the monitoring system, which can also cause an MOT fail.

Penalties for illegal tyres

You don't have to wait for the MOT to be caught out. Driving with illegal tyres can mean a fine of up to £2,500 and 3 penalty points for each tyre. Four bald tyres could add up to enough points to lose your licence.

Tyre advisories in MOT history

The MOT history of any car shows tyre advisories such as "close to legal limit" or "slight damage to sidewall". These are useful when you're buying a used car:

• A tyre advisory on the last test tells you the tyres probably need replacing soon, which is worth knowing when you negotiate.
• The same tyre advisory year after year can show an owner who leaves things to the last moment.
• Repeated uneven wear advisories can point to a suspension or alignment problem.

Our MOT advisory check groups recurring advisories by area, so you can see tyre warnings at a glance. Our guide to MOT advisories explains what to do about them.

Replace at 3mm, not 1.6mm

The legal limit is 1.6mm, but don't wait until you reach it. Check your tyres monthly, replace them at around 3mm, and look for cuts and bulges as well as tread. A quick check before the MOT is the easiest way to avoid one of the most common fails.