Tyre Tread Depth UK: Legal Limits & How to Check Yours
Tyre tread depth is one of the most important safety checks you can do on your car — and one of the most commonly overlooked. Here's what the UK law says, why the legal minimum isn't actually safe enough, and how to check yours in two minutes at home.
The UK legal minimum: 1.6mm
In the UK, the legal minimum tyre tread depth is 1.6mm, measured across the central three-quarters of the tyre, all the way around its circumference. Any tyre worn below this limit is illegal to drive on.
The consequences of being caught with illegal tyres are serious:
- Up to £2,500 fine per illegal tyre
- 3 penalty points per tyre (four illegal tyres = 12 points, enough to lose your licence)
- An automatic MOT fail
- Your car insurance may be invalidated in the event of an accident
Why 1.6mm is not actually safe enough
The legal minimum exists as a floor — not a target. The tyre industry, road safety organisations and independent testers consistently recommend replacing tyres at 3mm of tread — particularly for autumn and winter driving.
Why? Wet braking distance increases significantly as tread depth decreases. The grooves in the tyre tread are designed to channel water away from the contact patch so the rubber can grip the road. As those grooves get shallower, more water stays under the tyre — leading to aquaplaning and increased stopping distances.
The practical rule: At 3mm, start budgeting for new tyres. At 2mm, book them. Below 1.6mm, the car should not be on the road.
How to check tyre tread depth at home
The 20p coin test
The quickest check requires nothing but a 20p coin:
- Insert a 20p coin into one of the main tread grooves.
- If the outer band of the coin disappears into the groove, tread depth is above 1.6mm.
- If you can see the outer band clearly, tread is at or below the legal limit — replace immediately.
Check in at least three places across the width and several points around the circumference of each tyre. Uneven wear matters too.
A tread depth gauge (more accurate)
A digital tyre tread depth gauge costs around £5 from any motor factors shop and gives you a precise reading in millimetres. Push the probe into the tread groove and read the display. This is the most reliable method and worth doing at least twice a year.
New tyre tread depth: what to expect
A brand new tyre typically starts with 7–8mm of tread for a standard road tyre. Performance and sports tyres may start deeper. You can see how much life remains by tracking the depth over time — many drivers check every 3 months.
What about tyre wear indicators?
All modern tyres have built-in Tyre Wear Indicators (TWI) — small rubber bars moulded into the base of the tread grooves at a height of exactly 1.6mm. When the tread wears down to the level of these bars, the tyre is at the legal limit and must be replaced. Look for the triangular TWI marker symbol (▲) on the tyre sidewall — it points to the location of the wear indicator in the groove.
Free tread check in Ashford TW15
Not sure if your tyres need replacing? Pop in to our Feltham Road garage for a free tread depth check — we'll tell you exactly where you stand, with no sales pressure.