We meet this question crouched at a front wheel. A Glasgow driver, torch app on, checking a tyre they were told about at a service three weeks ago, wanting to know if they are already on the wrong side of the law.
Yes, it is illegal to drive on worn tyres in the UK. The famous number is 1.6mm, and it is real. But tread depth is only one of the ways a tyre becomes illegal, and in our experience it is not even the one that catches most people out.
This page covers the actual rules, how to check your own tyres in five minutes, and what to do if one fails, drawn from replacing tyres across Glasgow 24 hours a day, 7 days a week. To be clear at the start: this page sets out how UK road traffic law works in general terms, it is not legal advice, and anything specific to your own case is a matter for a solicitor.
The Short Answer
Yes. In the UK it is illegal to drive on worn tyres. Cars, light vans and trailers up to 3,500kg must have at least 1.6mm of tread across the central three-quarters of the breadth of the tread and around the complete circumference, under the Road Vehicles (Construction and Use) Regulations 1986.
That is the tread rule. A tyre can also be illegal with perfectly legal tread, on condition grounds such as cuts, bulges and exposed cord, on inflation and suitability grounds, on mixing grounds, and on load or speed rating grounds. The offence itself sits in Section 41A of the Road Traffic Act 1988. All of it is covered below.
What the Law Says About Driving on Worn Tyres
Two pieces of legislation do the work here, and they fit together simply.
The Road Vehicles (Construction and Use) Regulations 1986 set the technical requirements: how much tread a tyre must have, what condition it must be in, what it must be suitable for. Section 41A of the Road Traffic Act 1988 is the offence provision. It makes using a vehicle that breaches those tyre requirements a prosecutable matter.
The word that matters is using. The offence attaches to the vehicle being on a road at all. A worn tyre on a quiet run to the shops is the same offence as one on the M8, every day the car is driven.
The 1.6mm Minimum and Exactly Where It Is Measured
Here is the part most pages get half right. The law does not say “1.6mm somewhere on the tyre”. It says 1.6mm across the central three-quarters of the breadth of the tread, around the complete circumference.
Both halves of that rule bite. A tyre with 3mm in the middle grooves and a bare inside shoulder can still be illegal, because the shoulder sits inside the measured band. And a tyre that reads legal at three points but is bald in one band of its circumference is illegal too, because the rule runs the whole way round.
We find this exact tyre week in, week out: legal in the middle, worn through on the inside edge, and invisible to the owner until the wheel is turned to full lock. The middle grooves are where drivers look. The shoulders are where tyres fail.
Different Minimums for Different Vehicles
The 1.6mm figure belongs to one group of vehicles. The full picture:
| Vehicle | Legal minimum |
| Cars, light vans and trailers up to 3,500kg | 1.6mm across the central three-quarters, complete circumference |
| Goods vehicles over 3,500kg, buses and coaches | 1mm across the central three-quarters |
| Motorcycles over 50cc | 1mm across three-quarters of the breadth, visible tread elsewhere |
If you drive a van, check your plated weight rather than assuming. A 3.5 tonne van sits in the 1.6mm group. Sole traders running heavier vehicles are in the 1mm group, with the rest of the goods vehicle rules on top.
Six Ways a Tyre Becomes Illegal, Not Just One
Tread depth is the famous rule, and on our jobs it is the one that catches people least often. Here are all six, and any one of them alone is enough.
1. Tread Below the Legal Minimum
The 1.6mm rule as measured above: central three-quarters of the breadth, complete circumference. One band of the tyre below that line makes the tyre illegal, whatever the rest of it reads.
2. Cuts and Damage That Reach the Ply or Cord
The rule is precise. A cut is a defect where it is longer than 25mm or 10 per cent of the section width, whichever is greater, and deep enough to reach the ply or cord.
Worked through on a common size: a 205 section tyre gives 10 per cent as 20.5mm, so the 25mm figure is the one that applies. A shallow scuff is not the issue. Depth is. If cords show at the bottom of a cut, the tyre is done regardless of length.
3. Lumps, Bulges, Tears and Exposed Cord
Four separate defects in their own right: internal or external lumps and bulges, tears caused by separation of the tyre’s structure, and any exposed ply or cord.
A bulge deserves its own sentence, because drivers often treat it as cosmetic. A bulge means the casing is already damaged inside, with air pressing through broken structure. It does not improve, it does not wait, and it is illegal from the moment it appears. We set out what happens if you ignore a small crack or bulge separately.
4. Under-Inflation and Unsuitable Use
The Regulations also require a tyre to be suitable for the use the vehicle is being put to, and inflated so that it is fit for that use.
The practical version: a tyre run persistently soft is a compliance problem as well as a safety one, and so is a car tyre carrying loads it was never built for. The correct pressures live on the vehicle placard, in the driver’s door shut, the fuel filler flap or the handbook. Checking them monthly costs nothing, and regular tyre checks pay for themselves in fuel alone.
5. Mixing Radial and Cross-Ply on the Same Axle
The same Regulations forbid tyres of different structure, meaning radial and cross-ply, on the same axle. On modern cars this comes up rarely, since almost everything is radial.
The honest addition: mixing tread patterns or brands across an axle is poor practice even where it is not itself an offence. We see it most on used cars where a previous owner replaced one tyre at a time, and it is one of the things a fitter will point out on arrival. There is more on different tyres on the same axle if that is your situation.
6. The Wrong Load or Speed Rating
The load and speed rating fitted must be equal to or higher than the figure on the vehicle placard. Fitting lower is a compliance and insurance problem, not a preference.
Read it off the sidewall code. On 205/55 R16 91V, the 91 is the load index, worth 615kg per tyre, and the V is the speed rating, good for 149mph. For reference, H is 130mph, W is 168mph and Y is 186mph. We have found passenger casings fitted where a van’s plate called for a commercial C rated tyre, and that is this rule being broken in plain sight.
How to Check Your Own Tyres in Five Minutes
You do not need equipment to catch most problems. You need a 20p, good light and two minutes per wheel.
Walk round the car and look at each tyre’s face and both sidewalls, feeling lightly for lumps. Turn the steering to full lock and check the inside shoulders of the front tyres, because that is where wear hides. Then do the coin test on each tyre.
The 20p Test and What It Is Good For
Insert a 20p coin into the main grooves at three points around each tyre. If the outer band of the coin is visible above the tread, the tyre is at or near the limit and needs checking properly.
Now the limits of the test, which almost nobody publishes. It samples the main grooves at a few points. It does not measure the shoulders, and it does not prove compliance across the central three-quarters around the complete circumference. Treat it as a prompt to check properly, not a verdict. A tyre can pass the 20p test and still be illegal, most commonly on a worn shoulder or a bulged sidewall.
What a Fitter Checks That a Coin Cannot
On arrival at any job, the wheel gets more than a glance. Depth gauge readings at the inner, centre and outer positions, taken at several points around the tyre, because one number from one groove tells you very little. Inside shoulders checked at full lock. Sidewalls run by hand for bulges and tears, inside face as well as out. Valve and pressures checked against the placard.
The DOT code gets read too, for age. Its last four digits are the week and year of manufacture, so 2523 means week 25 of 2023, and an aged casing can be finished with tread to spare. Whether a tyre can be repaired is decided by inspection on arrival, and whether a particular tyre is legal is decided by measurement and inspection, which is why we check every wheel on arrival before we touch anything.
The Wear Patterns We See Most in Glasgow
Kerbing on tight Southside and West End streets takes the inside shoulder down while the middle grooves still read legal. Under-inflation wears both shoulders together. Over-inflation wears the centre band. Each pattern tells you something about the car as well as the tyre, and a shoulder-worn front pair usually means the tracking wants looking at before the new tyres go the same way.
1.6mm Is Legal, So Why Do the RAC Recommend 3mm?
Two numbers float around this subject, and they answer different questions.
| Figure | What it is |
| 1.6mm | The legal minimum. Below this you are committing an offence |
| 3mm | The replacement point recommended by the RAC and most safety bodies |
The 3mm recommendation is about physics rather than law. Tread grooves exist to clear water from under the tyre, and as they shallow, the tyre clears less with every rotation. Braking performance in the wet drops sharply below 3mm, well before the tyre becomes illegal. On wet Scottish roads, and on the M8 on a dark December evening, that gap between legal and effective is where the risk lives.
Our position, as a business that sells tyres and knows how that sounds: nobody is prosecuted for having 2mm, and nobody enjoys finding out what 1.7mm stops like in the rain. Plan the replacement inside that window, not at the end of it.
Worn Tyres and the MOT
Two separate enforcement routes exist, and drivers regularly blur them.
At MOT, a tyre below 1.6mm, cut as described above, bulged or showing cord is recorded as a major or dangerous defect and is an automatic fail. That is the annual snapshot.
The in-use requirement is the other route, and it applies every day the vehicle is on the road. Passing an MOT in March does not make a tyre legal in September, because tyres wear continuously, and a valid certificate is no defence for a tyre that has worn out since the test.
The call we take on this is always the same shape: a test booked in two weeks and a tyre that probably will not pass. Our honest answer is that a tyre worn to that point is a today problem, not a test-day problem. If a garage has told you all four need doing, what to do when a garage says you need four new tyres is worth a read first.
What It Costs If You Are Caught
A defective tyre can bring a fine of up to £2,500 and 3 penalty points per tyre, and the endorsement code CU30 stays on a licence for 4 years. Four illegal tyres can therefore multiply into something far more serious than one fixed sum. The GOV.UK guidance on tyre safety and the law sets out the driver’s side of it.
The points question is more complicated than most sources admit, so we cover the fine, the points and the insurance knock-on separately in our guide to the fine for driving on a bald tyre.
A Word on Part-Worn Tyres
Part-worn tyres are legal to sell in the UK under the Motor Vehicle Tyres (Safety) Regulations 1994, and must be sold with at least 2mm of tread across the full breadth around the entire outer circumference.
Note what that rule is. It is a supply requirement on the seller. It does not change the 1.6mm in-use limit that applies to you from the day the tyre goes on. A part-worn bought at 2mm is 0.4mm of wear away from illegal. Our position has not changed: a new budget tyre with a known start point is the better buy nearly every time.
What to Do If Your Tyres Are Already Illegal
Honesty first. If a tyre has exposed cord, a bulge or a tear, the safest answer is not to drive the car. A tyre in that state has already failed structurally, and the last miles on it are the most dangerous ones.
The mobile route exists for exactly this situation. Send a photo of the tyre sidewall on WhatsApp to 07955 533000 with your postcode. You get one total on the call, before the van moves, and nothing is added at the roadside. Payment is card at the vehicle, contactless included, after the work.
Across Glasgow and the Central Belt the average arrival is 30 to 45 minutes, and most drivers are back on the road within 20 to 40 minutes of the van arriving. Arrival times outside the Central Belt are given on the call for your exact location, and emergency tyre replacement in Glasgow runs the same way at any hour.
As a guide, a budget tyre fitted runs £60 to £100, mid-range £90 to £150, and premium from £140 to £280, in line with new tyres fitted at home across Scotland, with stock running from budget names like Landsail and Triangle through Falken, Hankook and Yokohama up to Michelin, Continental and Bridgestone. One thing we do not do is attend live motorway lanes or the hard shoulder, so a motorway failure is a recovery job first and a tyre job second.
Frequently Asked Questions
Is it illegal to drive on worn tyres in the UK?
Yes. A tyre below 1.6mm across the central three-quarters of its tread and complete circumference is illegal on cars, light vans and trailers up to 3,500kg. Cuts reaching the cord, bulges, exposed cord, wrong ratings and radial mixed with cross-ply on an axle are illegal too.
What is the legal tyre tread depth in the UK?
1.6mm for cars, light vans and trailers up to 3,500kg, measured across the central three-quarters of the breadth of the tread and around the complete circumference. Goods vehicles over 3,500kg, buses and coaches run to 1mm, as do motorcycles over 50cc with visible tread elsewhere.
Is 2mm of tread legal?
Yes, 2mm is above the 1.6mm legal minimum, so it is legal. It is also inside the zone where the RAC recommend replacement, because wet braking performance drops sharply below 3mm. Legal and sensible are two different lines, and 2mm sits between them.
Where on the tyre is tread depth measured?
Across the central three-quarters of the breadth of the tread, around the complete circumference. The shoulders inside that band count, which is why a tyre with a legal middle and a bare inside shoulder can still be illegal. One worn band anywhere around the tyre is enough.
Is a bulge in a tyre illegal?
Yes. Lumps and bulges, tears caused by separation of the structure and exposed ply or cord are all defects in their own right, whatever the tread reads. A bulge means the casing is damaged internally, and the safe answer is to stop driving on it.
Does a valid MOT mean my tyres are legal?
No. The MOT is a snapshot of the day of the test. The in-use requirement applies every day the car is on the road, and a valid certificate is no defence for a tyre that has worn out since the test.
Is the tread limit different for vans over 3,500kg?
Yes. Goods vehicles over 3,500kg run to a 1mm minimum across the central three-quarters, along with buses and coaches. Vans up to 3,500kg stay in the 1.6mm group, so check the plated weight rather than guessing.
Does the 20p test prove my tyres are legal?
No. It samples the main grooves at a few points and flags a tyre at or near the limit, which is useful. It does not measure the shoulders or the full circumference, and it says nothing about bulges or cuts. We gauge tyres properly on every job across Glasgow for exactly that reason.
Get an Illegal Tyre Replaced Tonight
Call or WhatsApp 07955 533000 with a sidewall photo and your postcode, any hour, in any weather. We are 24/7 Mobile Tyre Services, family run with fully certified technicians, based at 100 Jessie St, Polmadie, Glasgow G42 0PG, covering the City Centre, Southside, West End, Partick and Govan plus Paisley, Rutherglen and East Kilbride.
This page is general information about UK road traffic law rather than legal advice. What a fitter can tell you for certain is whether the tyre in front of them is fit to stay on the car, and that check comes with every job.
