Tyre tread depth and tyre safety checks

Tyre tread depth and tyre safety checks
Checking your legal tyre tread depth is one of the most important checks you can make on your car.

Having worn tyres means the only contact patch between you and the road is past its best. You could almost call it an accident waiting to happen. 

If the safety risks don’t hit home, maybe the risk of a £2,500 fine and three penalty points for a worn tyre will? That’s per tyre, too. If all four tyres are worn below the legal limit, you could potentially lose your licence and face a £10,000 fine.

What is the legal tyre tread depth?

The law states the minimum legal tyre tread depth for cars in the UK and Europe is 1.6mm across the central three-quarters of the tyre. The tread must meet this minimum requirement across its complete circumference. 

What is the expert-recommended minimum tyre tread depth?

Tyre and safety experts believe the 1.6mm legal minimum is insufficient to guarantee safety – most recommend a minimum tread depth of 3mm for tyre replacement. Tests by UK technical organisation MIRA found that, once tyres are below 3mm, stopping distances increase dramatically.

The difference in wet braking distance between a tyre worn to 3mm and one worn to 1.6mm can be as much as 44%. 

Worn tyres are particularly dangerous in the wet because a tyre’s tread helps disperse water away from the contact patch between tyre and road. If there’s less tread depth, less water can be shifted, increasing the risk of aquaplaning and losing grip.

In heavy rain, each tyre can shift one gallon of water every second, illustrating just how hard tyres work. Simply put, deeper tread means they can work better, improving grip. 

READ MORE: Should I buy winter tyres? Pros, cons and costs explained

How to check tyres are in a roadworthy condition - RAC expert tips

If you're unsure of the legal tyre tread depth and would like to know how to quickly and easily check to ensure your tyres are road legal than watch our quick and informative video with 13-year patrolman Matt Woodbridge.

Tyre tread depth has to be above 1.6mm to be legal. This must be the case for the middle three quarters of the tyre.

There are three ways to check this:

How to check tyre tread depth – the 20p test

The 20p test is a simple, quick and easy way of checking the tyre tread of your car's wheels. Just take a 20p coin and insert it into the tread grooves on the tyre. If you can't see the outer band on the coin, your tyres are above the legal limit.

However, if you can see the band and that section of the coin is still visible, your tyres could be unsafe and require professional inspection by a mechanic. Drivers should conduct the 20p test every month to check tyre tread depth.

Tyre tread depth – the 20p test

Checking tyre tread with tyre tread wear indicators

If the tyre is flush with these, it is below the legal limit and needs replacing.

Checking tyre tread with a tyre tread depth gauge

These are purpose made tools that quickly measure the depth of an individual tyre groove. These are available from our online store:

READ MORE: How to check your car's tyre pressure

What happens if you have an accident on illegal/bald tyres?

Driving with tyres that have a tread below the legal limit - or even worse, are bald - is dangerous. It can put you and other motorists at risk.

If you are involved in an accident and the car you are driving has illegal or bald tyres, you should be aware of the consequences.

Any insurance claim as a result of an accident could be invalidated, so potentially your insurer won't pay out any money any repairs needed to your vehicle.

However, driving with dangerous or defective tyres also puts drivers at risk of a fine of up to £2,500 and three points on their license. That is per tyre, so four illegal tyres could mean a fine of £10,000 and 12 penalty points.

You can buy tyre tread gauges that help you assess the tread depth of the tyre, plus you can also get more basic colour-coded tools that let you know if a tyre is legal or not at a glance.

For more information about tyres read our complete guide to tyre buying or our complete guide to tyre safety and maintenance.

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