MOT advisory explained
“Tyre worn close to the legal limit”
Every other advisory on your certificate is between you and your next MOT. This one is between you and any police officer who looks at your car — and it is the only one you can check yourself, in a minute, with a coin.
The tread depth is approaching 1.6 mm but has not reached it, so the tyre is still legal and the car passed. The margin between where you are and where you must not be is now measured in a couple of millimetres.
This is the one advisory worth acting on quickly, and not because of the MOT. Below the limit it is an offence you can be stopped for on any day of the year.
Each, fitted, including balancing, a new valve and disposal of the old tyre. Larger wheels and performance sizes sit well above this range.
Uneven wear changes the answer completely. A tyre worn on one edge is not just a tyre — it is telling you the geometry or the suspension needs looking at, and a new tyre fitted without fixing that will wear the same way.
A “tyre worn close to the legal limit” advisory means the tread depth is approaching the 1.6 mm minimum but has not yet reached it, so the car passes. Replacing a tyre costs £60–£120 each fitted. Of 46 million tracked tyre advisories, 9.9% later returned as a failure.
What 1.6mm actually means
The legal minimum for a car tyre in the UK is 1.6 mm of tread. That figure is precise in a way most people do not realise, and the precision matters when you are close to it.
- It applies to the central three-quarters of the tread. The outer eighth on each side does not count towards the measurement, which means a tyre can look acceptable across most of its width and still be illegal where it is measured. It also means the reverse: a worn outer shoulder does not automatically make the tyre illegal, though it does make it a warning.
- It applies around the entire circumference. Not at one point, not on average — the whole way round. A tyre with a flat spot or a band of heavier wear fails on that band alone, and rolling the car forward half a turn is part of any honest check.
- New tyres start at roughly eight millimetres. So a tyre at 3 mm has used around three-quarters of its usable tread, not a third. The remaining margin is much smaller than the numbers suggest, which is why the last couple of millimetres go faster than owners expect.
Most tyre manufacturers recommend replacement at 3 mm rather than at the legal figure, and the reason is water. Tread grooves exist to move water out from under the tyre, and their capacity falls as they get shallower. Wet stopping distances lengthen considerably between 3 mm and 1.6 mm, even though both are perfectly legal. The limit is where you stop being lawful, not where you stop being safe.
How to check it yourself, in a minute
This is the only advisory in the entire test you can verify without a garage, without a ramp and without asking anybody’s opinion.
The 20p test. Put a 20p coin into the main tread groove. If the outer band of the coin disappears completely, you have more than the legal minimum. If you can see that band, the tyre is at or near the limit and needs measuring properly. Do it in three places across the width and at three points around the tyre — the whole value of the check is finding the worst spot, not the average one.
Use the wear bars too. Every tyre has small raised blocks moulded into the bottom of the main grooves at exactly 1.6 mm. When the tread surface becomes flush with those blocks, the tyre is legally worn out. They are marked on the sidewall, usually by a small triangle or the letters TWI.
Which is what separates this advisory from every other one on your certificate. Brake pads also have a published limit — 1.5 mm — but reading it means taking a wheel off, so you have to ask someone and trust the answer. Here you need nobody. A coin and five minutes on the driveway gives you the same information the tester had.
Where this stops being about the MOT
Every other advisory in this section is a conversation between you and your next test. If you leave a worn bush or a misting damper, nothing happens until the car goes back. Tyres are different, and the difference is enforcement.
Driving on a tyre below 1.6 mm is an offence in its own right. It carries a fine of up to £2,500 and three penalty points, and — this is the part that catches people out — the penalty applies per tyre. Four worn tyres is not one offence with one fine. It is four, and twelve points is a disqualification.
It is enforceable on any day, not once a year. A roadside check needs no appointment and no test bay, and tread depth is one of the fastest things on a car to assess. The MOT is an annual snapshot; this is a standing requirement between snapshots.
Insurance is the quieter risk. An illegal tyre does not automatically void a policy, but it gives an insurer a reasonable question to ask after a collision, particularly one involving stopping distance in the wet. That is not a reason to panic. It is a reason not to run the last millimetre down.
How often does this advisory become a failure?
This can be measured rather than guessed. Following every tyre advisory forward to the same vehicle’s later tests, across 46 million of them — the largest single category in the whole record — shows what actually happened.
| What happened next | Tyres | Brake parts | Suspension |
|---|---|---|---|
| Became a failure at a later test | 9.9% | 9.4% | 18.7% |
| Ignored, no action taken | 30.5% | 36.1% | 37.1% |
| Fixed | 59.6% | 54.4% | 44.2% |
| Median advisory to failure | 376–379 days — the next MOT | ||
From the DVSA MOT testing bulk dataset (Open Government Licence v3.0): 829.7 million tests and 145.1 million advisories tracked to each vehicle’s later tests, from 46,001,206 tyre advisories. Tyres account for 23.8% of all recorded MOT defects, more than any other component group.
Tyres are the most flagged item on British cars and the least ignored. Thirty per cent get left, against thirty-six for brakes and thirty-seven for suspension. Given that tyres are also the cheapest of the three to put off, that is the opposite of what cost alone would predict.
Two things are true of tyres and of nothing else in this section. The limit is enforced away from the test, on any road, on any day. And the owner can check it personally, without equipment, without a garage and without taking anyone’s word for it.
Every other advisory asks you to accept a stranger’s judgement about a part you cannot see, and then wait a year to find out whether they were right. This one asks you to look. The six-point gap in ignore rates is what happens when a threshold is public, checkable and policed between tests.
The figure that does not move is conversion: 9.9%, almost identical to brakes. Roughly one in ten of these comes back as a failure whatever owners intend, which is a useful reminder that “I’ll do it before the MOT” is a plan a great many people also had.
When the tyre is not really the problem
A tyre that has worn evenly across its width has simply done its job. A tyre worn on one edge has been told to do something else, and replacing it without asking what will produce the same result again in a fraction of the time.
Wear on the inner or outer edge points at geometry. Tracking knocked out by a kerb or a pothole, or a worn suspension arm bush letting the wheel sit at the wrong angle. An alignment check afterwards is not an upsell here — it is the difference between one tyre and two.
Wear in the centre band means over-inflation; wear on both edges means under-inflation. Both are free to fix and both are worth checking monthly, because a tyre run consistently soft also runs hot, uses more fuel and fails sooner in ways that have nothing to do with tread.
Patchy or scalloped wear is a suspension signal. A damper that no longer controls the wheel lets it bounce rather than follow the road, and each bounce scrubs a small patch of tread. If the tyre feels wavy to the palm rather than smooth, that is what you are feeling.
What it costs
| Job | Price fitted | Notes |
|---|---|---|
| One tyre, common size | £60–£120 | Includes balancing, valve and disposal |
| Pair, same axle | £120–£240 | Usually the right call — see below |
| Alignment check afterwards | £40–£80 | Needed if the wear was uneven |
| Large or performance sizes | Well above | Wheel diameter drives the price hard |
Independent garage and tyre-fitter prices. This is one of the few jobs where a main dealer is rarely the natural choice, and where the same tyre varies more by size than by where it is fitted.
Replacing in pairs across an axle is usually right, and for a reason that is not commercial. Two tyres with different tread depths on the same axle grip differently, which matters most when braking hard in the wet — exactly the situation where you would rather both sides behaved the same. If one tyre is at the limit and its partner is close behind, doing both saves a second visit anyway.
New tyres belong on the rear, whichever wheels drive the car. That is counter-intuitive and it is the settled advice: a rear axle that loses grip before the front makes the car unstable in a way most drivers cannot correct, while the reverse simply makes the steering go light. If you buy two, ask for them on the back and the better pair moved forward.
Budget tyres are a real trade-off rather than a false economy. The gap between budget and premium shows up mainly in wet braking and in how long the tread lasts, so the cheapest tyre is not always the cheapest per mile. The EU label on every tyre gives a wet grip rating, and it is the one specification worth comparing before price.
| Worked example — one tyre, common family-car size | |
|---|---|
| Mid-range tyre, 16-inch | £68 |
| Fitting, balancing, valve and disposal | £15 |
| Typical total | ≈ £83 |
Sits in the middle of the £60–£120 range. A premium tyre in the same size costs noticeably more, and an 18- or 19-inch wheel moves the whole calculation well above this range regardless of brand.
Enter your reg — we’ll read your MOT history, decode each advisory and price it for your exact model.
What to do next
- Check all four yourself tonight. A 20p coin, three places across each tyre, three points around it. This is the only advisory you never need to take on trust, so there is no reason to.
- Look at how the wear sits, not just how deep it is. Even wear across the width means the tyre simply did its job. Wear concentrated on one edge means something else needs fixing first, or the new tyre goes the same way.
- Check the pressures while you are there. Free, two minutes, and it is the single most common cause of tyres wearing out early in the middle or at both shoulders. The correct figures are on a sticker in the driver’s door shut or the fuel flap.
- If you buy two, put them on the back. Whichever wheels drive the car. A rear axle with less grip than the front is the harder of the two situations to recover from.
Tyre advisory FAQ
What is the legal tyre tread depth in the UK?
1.6 mm, measured across the central three-quarters of the tread and around the entire circumference. Both parts of that definition matter: the outer eighth on each side does not count towards the measurement, and the depth must be met the whole way round rather than on average.
How do I check my tyre tread with a 20p coin?
Insert a 20p into a main tread groove. If the outer band of the coin is hidden, you have more than the legal minimum. If that band is visible, the tyre is at or near 1.6 mm and needs measuring properly. Check three places across the width and three points around the tyre, because the worst spot is what counts.
What is the penalty for driving on an illegal tyre?
A fine of up to £2,500 and three penalty points, and the penalty applies to each tyre separately. Four illegal tyres is four offences, which is twelve points and a disqualification. Unlike most MOT items, this is enforceable at the roadside on any day rather than once a year.
Should I replace tyres at 3mm instead of waiting for 1.6mm?
Most tyre manufacturers recommend it, and the reason is wet grip. Tread grooves clear water from under the tyre, and their capacity falls as they get shallower, so wet stopping distances lengthen considerably between 3 mm and the legal limit. Both depths are lawful; they are not equally safe.
Do tyres have to be replaced in pairs?
Not legally, but usually it is the right call. Two tyres with different tread depths on the same axle grip differently under hard braking in the wet, which is exactly when you want both sides behaving the same. If one is at the limit and the other is close behind, doing both saves a second visit.
Why is my tyre worn on one edge only?
Alignment or suspension rather than the tyre itself. Tracking knocked out by a kerb or pothole, or a worn suspension arm bush letting the wheel sit at the wrong angle, wears one edge far faster than the rest. Fitting a new tyre without correcting that produces the same wear again, so the alignment check afterwards is doing real work.
Should new tyres go on the front or the back?
On the back, whichever wheels drive the car. If the rear axle loses grip before the front, the car becomes unstable in a way most drivers cannot correct; if the front goes first, the steering simply goes light. Ask for new tyres on the rear and the better existing pair moved forward.
How often does a tyre advisory become an MOT failure?
Across 46 million tracked tyre advisories, 9.9% returned as a failure at a later test, 59.6% were fixed and 30.5% were ignored. That ignore rate is the lowest of any category — six points below suspension — which is what happens when a limit is published, checkable by the owner with a coin, and enforced at the roadside between tests.