Tyre tread depth and MOT tyre rules
Car tyres need at least 1.6mm of tread. Each illegal tyre can mean a fine of up to £2,500 and 3 points. What the MOT checks and how to judge tyres at a viewing.
Updated
The legal minimum tread depth for a car tyre in the UK is 1.6mm. That depth must be there across the central three-quarters of the tread, all the way around the tyre. Driving on a tyre below the limit can bring a fine of up to £2,500 and 3 penalty points, and that is per tyre. The MOT checks the same limit and a handful of other tyre faults. At a viewing, tyres also tell you how the car has been looked after, so they are worth five minutes of your time.
The legal minimum: 1.6mm
The Highway Code puts it this way: cars, light vans and light trailers must have a tread depth of at least 1.6mm across the central three-quarters of the breadth of the tread and around the entire circumference.
Three details people miss:
- Central three-quarters. The outer edges can be lower without breaking the rule, but a tyre worn on one edge usually has another problem (see uneven wear below).
- The whole circumference. A tyre that is fine in one spot and bald in another is illegal.
- Pressure counts too. The Highway Code also says tyres must be inflated to the manufacturer's specification for the load being carried.
Most car tyres have tread wear indicators: small raised bars in the main grooves that sit at 1.6mm. When the tread is level with the bars, the tyre is at the limit.
The penalty
Using a car with a defective tyre is a construction and use offence. On GOV.UK's list of endorsement codes it is CU30, which carries 3 penalty points. The maximum fine for a car is level 4 on the standard scale, which is £2,500.
The offence is counted per tyre, so four illegal tyres could in principle mean four sets of penalties. Points stay on a licence for 4 years from the date of the offence.
What the MOT checks on tyres
Section 5 of the DVSA inspection manual covers tyres. The tester inspects the tyres on the road wheels. The spare is not tested, though a tester who notices a defect on it should tell you.
| What the tester looks at | What fails |
|---|---|
| Tread depth | Main grooves below 1.6mm in the central three-quarters, anywhere around the tyre |
| Matching tyres | Different sizes, or different structures, on the same axle |
| Cuts | A cut longer than 25mm or 10% of the section width, whichever is greater, deep enough to reach the ply or cords |
| Lumps, bulges and tears | A lump, bulge or tear caused by separation or partial failure of the tyre structure, or cords exposed or damaged |
| Pressure warning system | A tyre pressure monitoring system that is malfunctioning or obviously not working, on cars first used on or after 1 January 2012 |
Since 20 May 2018 the tester also records a tyre that is obviously underinflated. That is a minor defect: it is listed on the result, but on its own it does not fail the car.
Tyres are usually among the cheaper items on a fail sheet to put right. That makes a tyre advisory a fair talking point when you agree a price, but rarely a reason on its own to walk away.
How to check tyres at a viewing
You need a coin, your eyes and a few minutes. Check all four tyres and the spare, if there is one.
The 20p test
Put a 20p coin into the main tread grooves at several points around each tyre. If the outer band of the coin is hidden, the tread is likely above the limit. If you can see the band, the tyre may be close to 1.6mm. It is a rough guide. A tread depth gauge from a motor factor is more accurate and cheap.
Uneven wear
Look across the whole width of each tyre.
- Worn on the inside or outside edge only: often a sign that the wheel alignment is out, or that a suspension part is worn. Alignment can be cheap to fix, but worn parts cost more.
- Worn on both edges: often a sign the tyre has run underinflated.
- Worn in the centre: often overinflation.
- Patchy or scalloped wear: can point to worn dampers or a wheel out of balance.
On the test drive, check that the car runs straight with your hands light on the wheel, and listen for a hum that changes with speed.
Tyre age
Every tyre has a DOT code on the sidewall. The last four digits give the week and year it was made: a code ending 2321 means the 23rd week of 2021. Rubber hardens with age, so an old tyre can have plenty of tread and still grip poorly. If the tyres look much older than the car's recent history suggests, ask why, and ask a tyre fitter to look at them.
Damage and mismatches
Run your eyes and hands (carefully) over the sidewalls for cuts, bulges and cracking. Check that the tyres on each axle are the same size and type. A mix of budget and premium tyres is legal, but it can say something about how the car has been looked after.
What tyres tell you as a buyer
Tyres are a quick read on maintenance. Four matching tyres with even wear suggest someone who replaced them in pairs and kept the alignment right. Mismatched, uneven or very old tyres suggest shortcuts elsewhere.
Read the car's MOT history for tyre advisories that came up two or three years running, and for advisories about suspension or steering that might explain uneven wear. Our MOT advisory checker explains the wording, and our MOT fail rate pages show which test areas fail most often for each model and age in Great Britain.
Heavier cars, such as many electric cars, can wear tyres faster. Our guide to the MOT for electric cars covers that, and what the MOT does not check covers the parts the test leaves out.
Frequently asked questions
What is the legal tyre tread depth in the UK?
For cars, light vans and light trailers it is 1.6mm across the central three-quarters of the tread, around the whole circumference.
What is the fine for a bald tyre?
The maximum fine for a car is £2,500 and 3 penalty points for each illegal tyre (endorsement code CU30).
Will my car fail its MOT on tyres?
It will fail if any road wheel tyre is below 1.6mm in the central three-quarters of the tread, has a large cut that reaches the ply or cords, has a lump or bulge, or does not match the other tyre on the same axle in size or structure. Cars first used on or after 1 January 2012 can also fail for a tyre pressure monitoring system that is malfunctioning or obviously not working. An obviously underinflated tyre is recorded as a minor defect, which does not fail the car on its own.
Does the MOT check the spare tyre?
No. The tester only inspects the tyres on the road wheels. If they notice a problem with the spare, they should tell you.
Is the 20p test accurate?
It is a quick rough check. If the outer band of the coin is visible, measure the tread with a gauge or ask a tyre fitter.