How to check your tyre tread
The UK legal minimum tyre tread depth is 1.6mm across the central three-quarters of the tyre and all the way around. The quickest home check is the 20p test: if the coin’s outer band disappears into the tread, you are probably legal, but if you can see it, get the tyre checked. Worn tyres are a common MOT failure and a serious safety and legal risk.
Your tyres are the only part of the car that actually touches the road, and the tread on them is what clears water, grips in the wet and helps you stop. Checking them takes a couple of minutes, needs no tools beyond a coin, and can save you from a fine, an MOT failure or worse. Here is how to do it properly.
The UK legal limit
In the UK the minimum legal tyre tread depth for cars is 1.6mm across the central three-quarters of the tread, measured all the way around the tyre. That wording matters. It is not enough for one small patch to be legal, the depth has to hold across the middle three-quarters and around the whole circumference. Anything below 1.6mm is illegal to use on the road and is an automatic MOT failure.
It is worth knowing that 1.6mm is the legal floor rather than a safe target. Braking distances in the wet grow noticeably as tread wears down, so plenty of drivers and safety organisations choose to replace tyres earlier, often around 3mm, to keep a sensible margin of grip in bad weather.
The 20p test
The simplest home check uses a 20p coin, which has a raised outer band around its edge. Push the coin into one of the main grooves of the tyre. If the outer band of the coin is hidden by the tread, your tyre is likely to be above the legal limit. If you can see the outer band, your tread may be close to or below 1.6mm, and the tyre should be checked by a professional who can measure it accurately.
Do not just test one spot. Check the inner, middle and outer grooves, and repeat at three or four points around each tyre, because tyres often wear unevenly. A tyre can look fine on the outside and be worn on an inner edge you cannot easily see. If any part fails the test, treat the whole tyre as suspect.
Looking for uneven wear
How a tyre wears tells you a lot about the car. Even wear across the tread is what you want. Wear that is heavier on one particular part usually points to something worth investigating.
| Wear pattern | Common cause |
|---|---|
| Both outer edges worn, centre fine | Under-inflation, the tyre running with too little pressure |
| Centre worn, edges fine | Over-inflation, the tyre running with too much pressure |
| One inner or outer edge worn | Wheel alignment or suspension needing attention |
| Patchy or scalloped wear | Worn suspension parts or wheels out of balance |
If you spot any of these, it is worth having the alignment and suspension checked, otherwise a new tyre will simply wear out the same way. Catching it early saves you from replacing tyres more often than you should.
Measuring more precisely
The 20p test is a good quick guide, but it only tells you roughly whether a tyre is above or below the limit. If you want an exact figure, an inexpensive tyre tread depth gauge measures the depth in millimetres and lets you track how each tyre is wearing over time. Many tyres also have small raised bars set into the bottom of the main grooves, called tread wear indicators. When the surface of the tread wears down level with those bars, the tyre is at or near 1.6mm and it is time to replace it. Using either method removes the guesswork.
When you do replace tyres, it is generally best to change them in pairs across the same axle so that grip is balanced from side to side. Fitting one new tyre next to a much older one can leave the car pulling or braking unevenly, so most garages will advise doing both together where they can.
Checking for damage
Tread depth is not the only thing to look at. Run your eyes over the whole tyre, including the sidewalls, for cuts, cracks, bulges or anything stuck in the rubber such as a nail or screw. A bulge in the sidewall is a particular warning sign, as it can mean internal damage that could lead to a sudden failure, and the tyre should be inspected without delay. Cracking in the rubber can appear on older tyres even if the tread still looks reasonable, since rubber ages over time.
Do not forget tyre pressure
Correct pressure keeps the tread in proper contact with the road, helps the tyres wear evenly and protects your fuel economy. The right figures for your car are in the handbook and often on a label inside the driver’s door frame or the fuel filler flap. Check pressures when the tyres are cold, ideally once a month and before long trips, and do not forget the spare if your car has one. Getting pressures right is one of the easiest ways to make a set of tyres last longer.
Why it matters for your MOT and the law
Tyres are one of the most common reasons cars fail the MOT, which is frustrating because they are also one of the easiest things to check yourself beforehand. Beyond the test, driving on an illegal tyre carries a fine of up to £2,500 and 3 penalty points for each tyre, so a car on four bald tyres is a serious risk to your licence as well as your safety. A few minutes with a coin can spare you all of it. If you want to understand the wider test, our guide to the difference between an MOT and a service is a good place to start, and our piece on what an MOT should cost explains the fixed maximum test fee.
A simple habit
Make tyre checks a monthly routine. Keep a 20p coin in the door pocket, glance over each tyre for wear and damage, check the pressures, and act on anything that looks off rather than leaving it. Tyres wear gradually, so a regular quick look means you replace them on your terms, before they become a legal problem or let you down in the wet.
Key takeaways
- The legal minimum is 1.6mm across the central three-quarters, around the whole tyre.
- The 20p test is a fast way to judge whether a tyre is close to the limit.
- Uneven wear on one edge often points to pressure, alignment or suspension issues.
- Tyres are a leading MOT failure, and each illegal tyre can mean a fine and penalty points.
Frequently asked questions
What is the legal tyre tread depth in the UK?
The minimum is 1.6mm across the central three-quarters of the tread and around the entire circumference of the tyre. Below that the tyre is illegal and would fail an MOT.
Should I really wait until 1.6mm to replace a tyre?
It is the legal minimum, not the ideal. Grip in the wet drops off well before that point, and many safety bodies suggest thinking about replacement around 3mm, so treat 1.6mm as the absolute last line rather than a target.
How often should I check my tyres?
A quick look roughly once a month and before any long journey is sensible. Check tread depth, pressures and for any cuts, bulges or objects stuck in the rubber while you are there.