What the law actually says
For cars in the UK, the legal minimum tread depth is 1.6mm across the central three-quarters of the tread, around the entire circumference of the tyre. It's not enough for one patch to pass — a bald strip anywhere around the tyre can put you under the limit.
The penalties have teeth: driving on an illegal tyre can mean a fine of up to £2,500 and three penalty points — per tyre. Four illegal tyres can, in principle, cost a licence.
The 20p test
The outer band of a 20p coin is roughly the legal limit. To check:
- Push the coin into a main tread groove.
- Look at it side-on. If the outer band of the coin is hidden, you have tread above the limit at that point.
- If you can see the band, the tyre may be at or below the legal minimum — get it measured properly.
- Repeat at several points around the tyre and across its width — inner, centre and outer grooves. Don't forget the inside edge, which wears unseen.
Why waiting for 1.6mm is a bad plan
Legal isn't the same as good. Wet braking and resistance to aquaplaning fall away noticeably as tread drops, which is why many manufacturers and road-safety organisations suggest replacing around 3mm rather than running to the wire. Between 3mm and 1.6mm, you're legal — but working with less and less margin in the rain.
What uneven wear is telling you
- Both edges worn, centre fine — likely under-inflation.
- Centre worn, edges fine — likely over-inflation.
- One edge worn — often alignment (tracking) or suspension geometry. Replacing the tyre without fixing the cause just buys the same problem again.
Make it a habit
Check tread and pressures monthly and before any long trip. It's the cheapest safety check in motoring — and if a tyre does need replacing, we'll fit the new one on your driveway, so the fix costs you minutes, not a morning.
Failed the 20p test?
We'll bring the replacement to you and fit it on the spot — usually same day.