Most UK drivers have heard of the 20p tyre test. Insert a 20p coin into the main tread groove of your tyre — if the outer band of the coin (the raised rim) is obscured by the tread, your tyres are above the legal limit. If the band is visible, they may be illegal. Simple, quick, and useful — but there’s more to the story.
What the 20p Test Actually Measures
The outer band of a 20p coin is approximately 1.6mm deep. The UK’s legal minimum tread depth for cars, light vans and trailers is — coincidentally — 1.6mm across the central three-quarters of the tread width and around the entire circumference. So the 20p test gives you a rough check against the legal limit.
Why 1.6mm Isn’t Safe Enough
Here’s what the test doesn’t tell you: tyre performance degrades significantly long before you hit 1.6mm. Research by TyreSafe and tyre manufacturers consistently shows that stopping distances in wet conditions increase substantially below 3mm. A car braking from 50mph on a wet road with 1.6mm tread needs around 8 metres more to stop than the same car with 3mm — enough to hit the car in front.
The 20p test tells you whether you’re above the legal limit. It doesn’t tell you whether your tyres are actually safe.
How to Check Tread Depth Properly
A proper tread depth gauge costs less than £5 and gives you an accurate reading in millimetres. Check at multiple points around the tyre and across its width — wear is often uneven, and a tyre can be above the legal limit in the centre but below it at the edges if there’s alignment or pressure issues.
What the Test Misses Entirely
Tread depth is only one measure of tyre safety. The 20p test tells you nothing about:
- Sidewall condition and cracking
- Internal structural damage from kerb strikes or potholes
- Tyre age and rubber degradation
- Uneven wear patterns that indicate mechanical problems
Use Our Free Tyre Checker Tool
For a more comprehensive check, try our Tread Depth Checker tool — or contact Logistic Move for a free tyre inspection anywhere in North Wales.