Guides
Tyre tread depth law in the UK
The legal minimum is 1.6mm, in a continuous band across the central three-quarters of the tread and around the entire circumference. Here is how to check it — and why acting at 3mm is wiser than waiting for the limit.
Last reviewed: August 2026 · LCDrive editorial team
What the law requires
For cars and light vans in the UK, every tyre must have at least 1.6mm of tread depth in a continuous band across the central three-quarters of the tread width, around the entire circumference. The outer quarters may legally sit below 1.6mm, but the central band may not — at any point around the tyre. The requirement applies to each tyre individually, so one worn tyre is one offence however new the other three are, and a tyre measuring 3mm at one spot and 1.4mm at another is illegal: the law judges the shallowest point, not the average.
How to check your tread
The 20p test
Insert a 20p coin into one of the main tread grooves. The raised outer band of the coin is roughly 2.6mm deep, so if the band disappears completely into the groove, the tread at that point is comfortably above the legal limit; if any part of it remains visible, the tread there may be at or near 1.6mm. Repeat at three points across the width and several points around the circumference, because tyres rarely wear evenly and the law cares about the worst point, not the best. Treat the coin as a screening check, not a measurement — where a groove looks marginal, confirm it with a gauge before driving on.
A tread depth gauge
A tread depth gauge costs a few pounds and reads in fractions of a millimetre. Rest the gauge across the tread, press the probe to the base of the groove, and read the depth. Record the lowest figure you find on each tyre — that is the number the law judges.
Tread wear indicators
Every road tyre carries tread wear indicators: small raised bars moulded into the base of the main grooves at intervals around the tyre, sitting 1.6mm above the groove floor. Their positions are usually marked on the sidewall with “TWI”, a small triangle or an arrow. When the tread surface sits flush with a bar, that part of the tyre is at the legal limit.
Why 3mm is the point to plan around
The law says 1.6mm. Industry safety guidance — from tyre manufacturers and UK motoring organisations — says plan the replacement at 3mm. The reason is water. Tread grooves exist to clear water from the contact patch, and as they shallow, the tyre clears less with every rotation. Wet grip declines slowly at first, then steeply: independent braking tests have repeatedly shown wet stopping distances lengthening sharply once tread falls below around 3mm, well before the tyre becomes illegal.
The 3mm figure is guidance, not law — a tyre at 2mm is legal. But a tyre at the limit is not performing the way it did new, and on a wet road the difference is braking distance, not a technicality. Budgeting for replacement at 3mm buys the months of best wet performance the last millimetre cannot — and with mobile fitting the swap happens at your home or workplace, not in a queue.
Tread depth and the MOT
A tyre worn below 1.6mm in the central band fails the MOT. It is recorded as a dangerous defect, and the advice that comes with that category is not to drive the vehicle until the tyre is replaced. That is precisely what Emergency roadside help is for — the replacement tyre comes to the car, so a dangerous defect never has to be driven on.
Testers can also record an advisory for a tyre that is legal but close to the limit — typically when tread is approaching the minimum and will not last until the next test. An advisory is not a failure, but it is a written record that you were told: worth acting on, not filing.
Penalties for illegal tyres
The penalty for driving on a tyre below the legal minimum can reach £2,500 and three penalty points — and each illegal tyre is treated as a separate offence, so the totals multiply with every worn tyre on the car.
There is a quieter cost as well: an insurer can question a claim if the vehicle was running on illegal tyres at the time of an incident. Set against either outcome, a replacement tyre is the cheap option.
Reading uneven wear
A tyre rarely wears evenly, and the pattern is diagnostic. Replacing a tyre without fixing the cause buys the same wear again — check the pattern before you buy.
| Wear pattern | Likely cause | What to do |
|---|---|---|
| Both outer edges worn, centre fine | Under-inflation — the tyre runs on its shoulders | Set pressures to the handbook figure and recheck monthly |
| Centre worn, edges fine | Over-inflation — the tyre runs on its crown | Set pressures to the handbook figure and recheck monthly |
| One edge only, inner or outer | Wheel alignment or suspension geometry out | Book an alignment check before fitting new tyres |
| Feathered, saw-tooth edges across the tread | Toe misalignment scrubbing the tread sideways | Book an alignment check |
| Flat spots or patchy wear | Wheel imbalance, a locked-wheel skid, or worn suspension | Have wheel balance and suspension inspected |
How often to check
Once a month, and before any long journey. Check all four tyres — and the spare, if you carry one — while the tyres are cold, and do pressures at the same time. With a 20p coin and a pressure gauge the whole routine takes a few minutes.
If a tyre is at or near the limit, replace it before it becomes a legal problem. You can browse replacement tyres by size or find the tyres that fit your car by registration. And because tread matters most when the roads are cold and wet, it is worth knowing how winter, summer and all-season tyres compare.