The legal minimum tyre tread depth in the UK is 1.6mm. That figure applies to cars, vans and light trailers up to 3,500kg, and the tread must meet it across the central three-quarters of the tyre's width, all the way around the wheel. This is set out in the law on tyre safety (GOV.UK) and reflected in Highway Code rule 89. It's one of the most checked items at the roadside and in the MOT, so it's worth understanding properly.
What the 1.6mm rule means
Tread is the grooved rubber that grips the road and clears water. As it wears down, stopping distances grow and the risk of aquaplaning rises sharply. The 1.6mm minimum is a legal floor, not a target. Tyre-safety charity TyreSafe and most manufacturers recommend changing tyres at around 3mm, because braking performance drops off noticeably between 3mm and 1.6mm, especially in the wet where it matters most.
How tread depth is measured
The 1.6mm is measured in the main grooves across the middle 75% of the tyre, around the complete circumference. A tyre can be legal in one spot and illegal in another if it's wearing unevenly, which is common with poor wheel alignment or incorrect pressures. Garages use a tread depth gauge; at home you can use the 20p test as a quick check between proper measurements. Many tyres also have moulded tread wear indicators, small raised bars in the grooves, which become flush with the tread when it reaches 1.6mm.
The penalties for illegal tyres
Driving with a tyre below the legal limit can cost you up to £2,500 and 3 penalty points per tyre. With four illegal tyres that's a potential £10,000 fine and 12 points, which is enough to lose your licence. Illegal tyres can also invalidate your insurance after an accident, an exposure that dwarfs the cost of new tyres.
- Tread below 1.6mm: illegal, MOT failure, fine and points.
- Cuts, lumps or bulges: illegal regardless of tread depth.
- Wrong size or type mixed on an axle: can also fail the MOT.
Why experts say 3mm, not 1.6mm
The legal limit and the safe limit aren't the same thing. Independent testing consistently shows that wet braking and aquaplaning resistance fall away well before 1.6mm, because shallow tread simply can't clear water fast enough. By the time a tyre reaches the legal minimum, its wet stopping distance can be many metres longer than a tyre at 3mm from the same speed, the difference between stopping in time and not. That's why TyreSafe and most manufacturers advise replacing at around 3mm rather than running tyres down to the legal floor. Treating 1.6mm as "still fine" is the mistake the recommendation is designed to prevent.
Legal tread depth by vehicle type
The 1.6mm figure applies to cars, light vans and light trailers, but it is not the only limit in UK law. Larger vehicles and motorcycles have their own minimums, set by the same regulations and summarised on GOV.UK.
| Vehicle | Legal minimum tread | Where it is measured |
|---|---|---|
| Cars, light vans and light trailers (up to 3,500kg) | 1.6mm | Central three-quarters of the width, around the whole circumference |
| Larger vehicles and trailers over 3,500kg | 1mm | Central three-quarters, with the original tread pattern visible on the rest |
| Motorcycles over 50cc | 1mm | Across three-quarters of the width, with the original tread visible on the rest |
| Mopeds up to 50cc | Visible tread | The original tread pattern must be clearly visible |
The regulation behind these figures is regulation 27 of the Road Vehicles (Construction and Use) Regulations 1986, as amended. It also outlaws cuts deep enough to reach the cords, lumps and bulges, exposed ply or cord, and tyres unsuitable for the vehicle or for the tyres on the same axle.
In practice, the tread figure is the one most drivers know, and the condition rules are the ones that catch them out. Note that the space-saver spare in your boot is covered by the same rules the moment it is fitted.
Tread depth and the MOT
A tyre below 1.6mm anywhere in the central three-quarters is an MOT failure; a tyre close to it is usually recorded as an advisory. The tester measures with a gauge across the tread and checks the full circumference, so a tyre that is legal at the top can still fail on a bald patch at the bottom.
The MOT tyre inspection also covers the things the tread figure does not: cuts, lumps, bulges, exposed cord, tyres of different sizes or construction on the same axle, and a tyre pressure warning light that stays on in newer cars. The full standard is in the MOT inspection manual on GOV.UK.
An advisory for tread close to the legal limit is not a fail, but it is a countdown. A tyre with 2mm left may reach 1.6mm within a few thousand miles, and it has already lost most of its wet-weather grip.
Treat it as a replacement due before winter rather than a note to file. Our guide to MOT tyre checks explains what the tester looks for.
Remember that passing the MOT proves the tyres were legal on that day only. You can be prosecuted for an illegal tyre the week after a pass, and the certificate is no defence.
Reading the wear pattern
Where a tyre is worn tells you why, and fixing the why is the only way the next set lasts. Measure at the inner edge, the centre and the outer edge of each tyre, not one spot, and compare the three numbers.
| Wear pattern | Most likely cause | What to do |
|---|---|---|
| Both edges worn, centre good | Under-inflation | Set pressures monthly; check for a slow leak on that wheel |
| Centre worn, edges good | Over-inflation | Use the placard figure, not the sidewall maximum |
| One edge only, usually the inner | Wheel alignment (camber or toe) | Have the geometry checked before fitting new tyres |
| Patchy or scalloped around the tyre | Worn shock absorbers or a balance problem | Suspension inspection, then rebalance |
| Flat spot in one place | Locked wheel under heavy braking, or long storage | Usually replacement if it causes vibration |
Inner-edge wear is the one that catches drivers out at the roadside, because it is invisible unless you turn the steering to full lock or run a hand across the tread. It is also the most common reason a tyre that looks fine from the kerb is illegal. See why tyres wear unevenly.
If your tyres are close to the limit
Don't wait for the MOT. If a quick check shows you're near 1.6mm, get the tyres replaced, because the safety loss has already happened well before the legal limit. Our mobile tyre fitters come to your home, work or a safe place off the road, so you never have to drive on a borderline or illegal tyre to reach a garage. We work from one base at Brent Cross, NW2; further out, call and we will tell you whether we can take the job.
