Tyre Tread Depth: The 20p Test Every Driver Should Know

Tyres are the only part of your car actually touching the road, yet they're one of the most neglected things drivers check. Most people can tell you when their last service was, but ask them their tyre tread depth and you'll usually get a shrug. That's a problem — worn tyres aren't just an MOT fail waiting to happen, they're a genuine safety risk in the wet.

Here's what you actually need to know.

The legal minimum — and why it's not enough

UK law requires a minimum tread depth of 1.6mm across the central three-quarters of the tyre, around the entire circumference. That's the legal line, but it's not the safety line. Independent testing consistently shows stopping distances in the wet increase sharply below about 3mm — by the time you hit the legal minimum, your stopping distance can be significantly longer than a tyre with healthy tread. Many manufacturers and safety bodies recommend replacing at 3mm, not waiting until 1.6mm.

How to check tread depth yourself

The classic trick is the 20p test: insert a 20 pence coin into the main tread grooves. If the outer band of the coin is covered, you're likely above 3mm and fine for now. If the band is visible, it's worth getting checked properly. Do this at three points across each tyre — outer edge, centre, and inner edge — because wear is often uneven, and a tyre can look fine in the middle while being dangerously low at the edge.

Signs your tyres need attention

• Uneven wear across the tyre. More wear on one edge than the other usually points to incorrect tyre pressure or a wheel alignment issue — worth fixing the cause, not just the symptom.
• Cracking or perishing in the sidewall. Even with plenty of tread left, age and UV exposure make rubber brittle over time — a genuine blowout risk.
• A bulge or lump in the sidewall. This means the internal structure is damaged, usually from hitting a pothole or kerb. Needs immediate replacement, not just monitoring.
• Vibration through the steering wheel. Can mean a wheel balance issue, but also worth ruling out uneven or damaged tyres.
• The car pulling to one side. Often tyre pressure or alignment related, but always worth a proper check.

Pressure matters as much as tread

Under-inflated tyres wear unevenly, increase fuel consumption, and generate more heat — a major cause of blowouts on motorway journeys. Over-inflated tyres reduce the contact patch with the road, hurting grip and causing wear down the centre of the tread. Check pressures monthly when the tyres are cold, using the figures in your door sill or handbook, not the number printed on the tyre itself.

What our tyre check covers

Our tyre check is free — we measure tread depth across all four tyres, inspect for sidewall damage and uneven wear, and check pressures. If replacement or a puncture repair is needed, we fit new tyres for all makes and models and balance them properly before you leave. If wear looks uneven, we'll flag whether it's worth pairing with a check of your suspension and steering, since that's the usual root cause.

Don't wait for the 20p test to fail

Tyres are one of the cheapest ways to genuinely improve your safety on the road — and one of the easiest things to put off. If it's been a while since anyone actually checked yours, get a free tyre check online, or drop by our Hayes garage — 235 Yeading Lane, UB4 9AD. Questions first? Get in touch here.