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How to check tyre tread depth

As a driver, it is your responsibility to check and maintain your tyre tread depth. This is our guide on how to check tyre tread.

28 March 2024

Tyre tread depth - a guide

Checking tyre tread is a quick and easy job. Taking the time to do so is important because it keeps you and your passengers safe. It also keeps your car road legal. When checking your tread depth, the first thing to consider is the legal tyre tread depth in the UK.

The legal minimum tyre tread in the UK

The legal tyre tread on a car in the UK is 1.6 millimetres. This means that the minimum depth of tread across the central three quarters of the tread and around the complete circumference of the tyre must be no less than 1.6mm. It’s also best practice not to wait until your tread gets to the legal limit to replace the tyre.

Check your manufacturer’s vehicle handbook for specific information on when they advise replacing the tyre. Certain safety experts and carmakers suggest replacing the tyre when the tread reaches 3mm.

Tread depth (mm) Worn % (approx.) Grade
8mm 0% Perfect
7mm 15% Good
6mm 31% Good
5mm 47% OK
4mm 62% OK
3mm 78% Monthly inspection needed
2mm 94% Nearly worn
1.6mm 100% Legal limit

Read on to learn how to check your tyre tread depth. You can visit your local Arnold Clark Service department for a free tyre safety check.

Check tread depth using a manual or digital gauge

An image of someone holding a tyre pressure gauge into a tyre's tread

You can use a manual or digital tyre tread depth gauge to check your tyres. Turn your steering wheel full lock to ensure you have a good view of the whole width of the tyre. Place the gauge on the surface of the tyre and push the end of the gauge down. As you push down, the ‘needle’ will stick into the tyre groove.

The top of the gauge then gives you the tread reading in millimetres. Digital gauges are similar in how they are used. The main difference is that the reading will be shown on a digital screen.

Check wear markers on the tyre

An image of a tyre with yellow circles highlighting where the wear markers can be found on the tyre tread

Every tyre comes with tyre wear markers. These are marks evenly spaced across the tyre tread and help identify how much tread has worn down. The types of markers will vary depending on the brand and type of tyre your car needs.

The markers are set to 1.6mm and should never be flush to the grooves of the tyre tread. If they are, it means it is most definitely time for a new tyre. This is because the tyre is at the legal limit and you could be breaking the law.

Check using the 20p tyre test

A close up of someone holding a 20p into the tread of a tyre to check the depth

You can also check your tyre tread depth with something most of us will have in our pocket right now… a 20 pence coin. The edges of 20p coins in the UK are 3mm deep. You can insert the coin into the tyre groove and if you cannot see the outer band on the 20p, you still have 3mm of tread.

If you insert the 20p into the groove and the outer band is still visible, your tyres could be below the legal limit. This could mean that not only are they illegal but also unsafe. If this is the case, we would recommend you pop in in to your local Arnold Clark branch for a professional inspection.

Why checking your tyre tread depth is important


Checking your tyre tread depth is something which every car owner must do. It is one of the most important checks to ensure your car is road legal. The tread of a tyre is designed to maintain contact with the road surface. Worn down tyre tread reduces the tyre’s capacity to grip the road. This can lengthen stopping distances and raise the risk of aquaplaning, increasing the likelihood of an accident.

In a recent study carried out by Peter Wells and the Centre for Automotive Industry Research at Cardiff University, it was found that worn tyres are more detrimental to a car’s stopping distance than the driver being under the influence of alcohol.[1]

The study concluded that consuming alcohol and driving at 70mph would increase the distance taken to stop the car by 12.4ft. Driving with 1.6mm of tread (tread at the legal limit) could potentially increase the stopping distance by 89ft. That is 76.6ft more of a distance to stop. This should put into perspective just how dangerous driving with worn tyres is.

The law

In the UK, if you drive with worn tyres and are caught by the police, you are at risk of a £2,500 fine per illegal tyre. This also goes alongside three penalty points per illegal tyre. See the below table for a breakdown of penalty points and fines per number of illegal tyres:

No. of worn tyres No. of penalty points Fine (£)
1 3 £2,500
2 6 £5,000
3 9 £7,500
4 12 £10,000

It’s also important as a car owner to regularly inspect your tyres. You should check for any bulges, cuts or tears on the tyre wall. Tyres with cuts which cover more than 25mm or 10% of the width of the wheel can also be deemed illegal by Police. This also means that you could face penalty points and receive a fine of up to £2,500.

What causes tyre wear?

There are many different factors which cause tyre tread to wear down, the main one being tyre usage over time. There are some factors which can lead to premature tyre wear.

Incorrect tyre pressure

If your tyres are over or under-inflated, this can lead to uneven tyre tread. Underinflated tyres cause heightened friction and heat build-up against the road surface. This hastens the deterioration of the tread on a tyre. Overinflated tyres may wear down the centre of the tyre tread before the edges. This can lead to premature tyre wear on one part of the tyre.

To prolong a tyre’s life, car owners should regularly monitor their tyre pressure. Check your own specific model for accurate tyre pressure levels. Ensuring your tyre is at the correct pressure enhances fuel efficiency. It also improves vehicle safety.

Driving style, mileage and overloading

Individual driving style and mileage also play a huge part in causing tyre wear. Aggressive acceleration, braking and cornering can increase the rate at which they degrade. You should keep this in mind when you are driving and adjust your driving style accordingly.

If you do a lot of driving every day, you may also notice that your tyres wear down quicker than other people’s. This is simply because of the frequency with which the tyres are being used. Carrying a heavy load often can also contribute to an increased risk of premature tyre wear.

Wheel misalignment

If your wheels are misaligned, uneven tread wear is almost unavoidable. It leads to excessive friction on particular areas of the tyre and results in irregular or abnormal tread patterns. Irregular tread patterns can include:

Worried about misaligned tyres? Call our Service department or pop into your nearest branch today. We can inspect and address any alignment issues. Avoid premature tyre replacement and get back out on the roads in no time!

Tyre design and composition

Lastly, tyre design and composition is often overlooked. The durability can be dictated by type of tyre, materials used and tread pattern. The tyre’s material will dictate how quickly it will degrade.

High-performance tyres are often made with softer rubber compounds. This helps them to achieve better grip on the road. These softer rubber compounds may wear out faster than the harder rubber compounds found in all-season tyres. Some tread patterns are also designed for specific road conditions, i.e., winter tyres. These types of tyres may wear differently depending on usage.

Need new tyres?

Did you know that we also sell tyres? Head over to Arnold Clark Autoparts to browse a selection of tyres with prices that won't wear you down. We stock almost every brand or size of tyre on demand and offer next working day delivery if you order before 2pm! If you can’t find what you’re looking for, contact us or call now on 0141 950 4018.


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