How to Check Your Tyre Tread Depth — and Why It Matters

Your tyre tread depth is the single most important safety feature on your car when it comes to grip on wet roads. In the UK, the legal minimum tread depth is 1.6mm across the central three-quarters of the tyre, around the entire circumference. Driving on tyres below this limit is illegal and carries a fine of up to £2,500 and 3 penalty points per tyre — meaning all four illegal tyres could cost you £10,000 and a driving ban.

This guide explains exactly how to check your tread depth at home, why the experts recommend changing at 3mm rather than the legal limit, and what to do if your tyres are worn. If you need help, our mobile tyre fitting team covers Harlow, Bishop's Stortford, Cambridge and the whole of the East of England.

Why Tyre Tread Depth Matters

Tyre tread is designed to disperse water from beneath the tyre so the rubber stays in contact with the road. As tread wears down, the tyre's ability to clear water drops sharply, which increases stopping distances and the risk of aquaplaning.

Independent testing by the road safety charity TyreSafe found that stopping distances from 70mph in wet conditions increased by 44% when tread depth dropped from 3mm down to the 1.6mm legal limit. At motorway speeds, that extra distance can be the difference between stopping in time and a serious collision.

The 3mm Recommendation

Most tyre manufacturers, motoring organisations and road safety bodies recommend replacing tyres when tread reaches 3mm rather than waiting for the 1.6mm legal minimum. The performance difference between 3mm and 1.6mm is significant, while the difference between 4mm and 3mm is much smaller.

How to Check Your Tyre Tread Depth

There are three reliable ways to check your tread at home:

The 20p Test

The quickest method uses a 20p coin. Insert the coin into the main tread groove of your tyre. The outer band of the 20p is roughly 1.6mm wide. If you can see the outer band above the tread, your tyre may be illegal and must be checked by a professional immediately. If the band is hidden, your tread is above the legal limit — but ideally above 3mm.

Tread Depth Gauge

A digital or manual tread depth gauge costs around £10 and gives an accurate reading. Measure in several places around each tyre, as wear is rarely even. Pay particular attention to the inner and outer edges, where alignment or pressure issues often show up first.

Tread Wear Indicators

Many tyres have tread wear indicators (TWI) moulded into the grooves. These small raised bars sit at 1.6mm. When the tread wears down to the level of these bars, the tyre has reached the legal limit and must be replaced.

What Causes Uneven Tyre Wear

If your tyres are wearing unevenly, there is usually an underlying cause that should be fixed before you fit new rubber, otherwise the new tyres will wear just as quickly.

• Under-inflation causes wear on both outer edges of the tyre
• Over-inflation causes wear in the centre of the tread
• Misaligned wheels cause feathered or scalloped wear across the tread
• Worn suspension can cause cupping or bald patches

If you spot uneven wear, our mobile puncture repair and tyre check service can inspect your tyres at your home or workplace and advise on the cause.

When to Replace Your Tyres

Even if your tread is legal, you should replace tyres if they are more than 10 years old, if there are cracks in the sidewall, or if there is a bulge or cut. Age and damage degrade the rubber even when the tread looks fine. See our tyre age guide for more detail.

Keep Yourself Legal and Safe

Checking your tread takes two minutes and could save your licence — or your life. Make it part of your monthly routine alongside checking pressures with our tyre pressure guide.

If you're unsure about your tread depth, call us on 01279 881234. We'll come to you anywhere across Essex, Hertfordshire and Cambridgeshire and check all four tyres for free as part of any visit — and if you need new tyres, we carry most major brands and sizes on the van ready to fit on the spot.