LEGAL TREAD DEPTH & THE 20p TEST

What the law 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. One good patch is not enough: a bald strip anywhere around the tyre can put you under the limit.

The penalties are applied per tyre: a fine and three penalty points for each illegal tyre. Four illegal tyres can, in principle, cost you your licence.

The 20p test

The outer band of a 20p coin is roughly the legal limit. To check:

1. Push the coin into a main tread groove.
2. Look at it side-on. If the outer band of the coin is hidden, you have tread above the limit at that point.
3. If you can see the band, the tyre may be at or below the legal minimum. Get it measured properly.
4. Repeat at several points around the tyre and across its width: inner, centre and outer grooves. Don't forget the inside edge, which wears out of sight.

Why waiting for 1.6mm is a bad plan

Legal is not the same as good. Wet braking and resistance to aquaplaning fall away noticeably as tread drops, which is why many tyre makers and road-safety bodies suggest replacing at around 3mm. Between 3mm and 1.6mm you are legal, but 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 or suspension geometry. Replacing the tyre without fixing the cause buys the same problem again.

Make it a habit

Check tread and pressures monthly and before any long trip. If a tyre does need replacing, we fit the new one on your driveway, so the fix costs you minutes and not a morning.