When to Replace Car Tyres: UK Tread Law and Warning Signs

By Matthew Croxford · 13 Oct 2026 · Updated 20 Oct 2026

Short answer: Replace car tyres once tread falls to around 1.6mm, the UK legal minimum across the central three-quarters of the tyre, measured all the way round. Below this you risk an MOT failure and fines up to £2,500 and 3 penalty points per tyre. Manufacturers recommend changing at around 3mm for safer wet-weather grip, rather than waiting for the legal cut-off.

Knowing when to replace car tyres isn't just about ticking a legal box. It's the single easiest bit of maintenance to get wrong, because a tyre can look perfectly fine from the kerb while being dangerously close to the limit. The UK's tread depth law has applied in its current form for decades, so nothing here is new, but plenty of drivers still misread it, ignore the warning signs, or get caught out buying a used car with tyres that are quietly on their last legs.

The UK tread depth law: what 1.6mm actually means

The legal minimum tread depth for a car tyre in the UK is 1.6mm, and that figure must be present across the central three-quarters of the tyre's width, measured all the way round the circumference. It isn't enough for the middle groove to look healthy while the shoulders are worn through; one bald patch anywhere on that central band makes the whole tyre illegal, according to GOV.UK. The same rule covers vans and light trailers up to 3,500kg. Motorcycles and larger passenger-carrying vehicles have their own, different minimums.

Fall below 1.6mm and you're not just risking an MOT failure, you're driving illegally. The penalty is severe by UK standards: up to £2,500 and 3 penalty points, per tyre. Run on four illegal tyres and, in theory, that's £10,000 and 12 points in one stop, which is enough to put a licence at real risk under the totting-up rules.

Fines and penalty points are set out in law and can be revised, so always check the current position on GOV.UK rather than relying on a figure from memory.

Why 3mm, not 1.6mm, is the number worth watching

Legal and safe are two different things. Once tread wears down towards the legal floor, a tyre's ability to clear water from under the contact patch drops away, and wet-weather braking performance and resistance to aquaplaning fall off noticeably well before you hit 1.6mm. That's why tyre manufacturers and safety campaigners generally recommend replacing tyres at around 3mm rather than waiting for the legal cut-off, particularly if you cover a lot of motorway miles or drive regularly in the rain.

Think of 1.6mm as the point at which the law steps in, not the point at which you should start shopping. By the time a tyre reaches the limit, you've already been driving on reduced grip for months.

The 20p test, and why it's only a starting point

The classic DIY check is to insert a 20p coin into the tread groove. If the outer rim of the coin is still visible, tread is getting low and it's worth a proper measurement with a depth gauge. It's a useful quick check, but it only tells you about the point where you insert the coin, not the whole tyre. Always check several points across the width and round the circumference, especially the inner edge, where misalignment often causes wear that's invisible from the outside of the car.

Five wear signs that mean it's time for new tyres

Tread wear indicator bars flush with the tread. Every tyre has small raised bars moulded into the base of the main grooves at the 1.6mm mark. If the tread is level with these, you're already at the legal limit, not approaching it.
Uneven wear across the tyre. Wear concentrated on one edge usually points to incorrect tyre pressure or a wheel alignment problem, and it often means the tyre is illegal on one side while looking fine in the centre.
Cracking or perishing in the sidewall rubber. This is an age issue rather than a mileage issue. A tyre with plenty of tread left can still be unsafe if the rubber has hardened and cracked from years of sun, heat and ozone exposure.
Bulges, lumps or cuts. Any damage to the tyre's structure, including a bulge from an impact with a pothole, makes it unroadworthy regardless of how much tread remains, and it will fail an MOT on the spot.
Vibration through the steering wheel, or the car pulling to one side. This can point to uneven wear, a damaged tyre, or a wheel balance or alignment fault, and it's worth investigating before it gets worse.

How to read the markings on a tyre

The sidewall of a tyre carries a compact code that tells you everything you need to buy the right replacement. A typical example reads something like 205/55 R16 91V, and each part means something specific:

205 is the tyre's width in millimetres, measured from sidewall to sidewall.
55 is the aspect ratio, the tyre's sidewall height expressed as a percentage of its width.
R stands for radial construction, which is standard on virtually every modern car tyre.
16 is the rim diameter in inches, so this tyre fits a 16-inch wheel.
91 is the load index, a code (not a direct weight figure) that relates to the maximum load the tyre can carry per wheel.
V is the speed rating, a letter that indicates the maximum speed the tyre is rated for when correctly inflated and loaded.

Beyond the main size code, you'll also find a DOT date stamp (the last four digits show the week and year of manufacture), an E-mark confirming European type approval, and, on the tyre's label at point of sale, ratings for fuel efficiency, wet grip and external noise.

Why the load index and speed rating matter when you replace

When you're buying replacements, match the original size, load index and speed rating, or go higher, never lower, than what's specified in your vehicle's handbook or on the plate inside the driver's door. Fitting an undersized or under-rated tyre isn't just a performance compromise, it can be an MOT failure and, in the event of a claim, a reason for an insurer to query cover. If you're only replacing one or two tyres rather than a full set, it's also worth sticking to a matching tread pattern on the same axle, since mismatched tyres can affect handling, particularly on four-wheel-drive cars.

Why worn tyres matter when you're buying a used car

Tyres are one of the easiest things for a seller to gloss over and one of the easiest things for a buyer to overlook on a test drive, especially if the weather's dry and the car feels fine at 30mph in a car park. A car that's chewed through a set of tyres unevenly is often telling you something about its alignment, suspension or past driving style, and that's worth factoring into any offer.

Before you view a car, it's worth running a check on the registration. A free check on our reg lookup tool pulls together the full MOT history, including every test result, advisory and failure reason, plus the mileage recorded at each individual test, the DVLA vehicle details, any outstanding safety recalls and a free market valuation as a general guide. If previous MOTs flag repeated advisories about tyre wear, cracking or tread depth, that's a pattern worth asking about rather than a one-off.

Tyre condition is only part of the picture, though. For the background that genuinely changes whether a car is worth buying at all, such as whether it's recorded as stolen, has been written off, is still carrying outstanding finance, or has had multiple keepers, imports or exports, it's worth running our vehicle history check, which draws on data from Experian. If you're buying through a dealer or the MotifyMe marketplace and want to spread the cost, you can also be introduced to car finance, subject to status and affordability; this route isn't available on a private sale, so it's worth knowing which category your purchase falls into before you commit.

Keeping on top of tyre condition

Tyres don't wear at a steady, predictable rate, so a quick visual and a depth check once a month, and always before a long trip, is a sensible habit rather than an overcautious one. Check pressures cold, inspect the full circumference rather than just the bit you can see without crouching down, and don't wait for the wear indicators to be flush before you start pricing up replacements. For more on running and maintaining a used car, our guides cover the other checks worth doing before you buy or sell.

Frequently asked questions

What is the legal minimum tread depth for car tyres in the UK? The legal minimum is 1.6mm, which must be present across the central three-quarters of the tyre's width, measured all the way round the circumference, according to GOV.UK.

What is the penalty for driving on illegal tyres? Each illegal tyre can bring a fine of up to £2,500 and 3 penalty points, so four illegal tyres could in theory mean £10,000 and 12 points in one stop.

At what tread depth should I actually replace my tyres? Manufacturers and safety campaigners generally recommend replacing tyres at around 3mm rather than waiting for the 1.6mm legal cut-off, especially for motorway or wet-weather driving.

How does the 20p test work for checking tyre tread? Insert a 20p coin into the tread groove, and if the outer rim is still visible, tread is getting low and worth measuring properly with a depth gauge, checking several points across the tyre.