Tyre tread depth is one of those things most drivers never think about until an MOT tester points it out. That’s a shame, because checking it at home takes about two minutes and needs nothing more than a coin you probably already have in the car. This guide walks through the methods, what the numbers actually mean, and how to spot trouble before it becomes a fine.
Quick Answer
To check tyre tread depth at home, insert a 20p coin into the main grooves of the tyre. If the raised outer band of the coin is hidden, your tread is above the 1.6mm legal minimum. If you can see that band, the tyre is likely illegal and needs a professional inspection. For a more precise reading, a tread depth gauge measures the exact depth in millimetres. Check all four tyres, at several points around each, since wear is rarely uniform.
Key Takeaways
- The UK legal minimum tyre tread depth is 1.6mm across the central three-quarters of the tyre.
- A 20p coin works as a quick check because its outer band sits at roughly 2mm.
- Most safety experts, including the RAC, recommend replacing tyres at 3mm rather than waiting for 1.6mm.
- Driving on an illegal tyre carries a fine of up to £2,500 and 3 penalty points per tyre.
- Uneven wear across a tyre often points to alignment or pressure problems, not just age.
- Check tread when tyres are cold and the car is parked on level ground.
Why Tread Depth Actually Matters
Tread is the patterned rubber that grips the road. Its main job is shifting water out from under the tyre so you keep contact with the surface in the wet. As tread wears down, that ability fades fast.
The difference is bigger than most people expect. According to the RAC, tests by the UK organisation MIRA found that wet braking distance can increase by as much as 44% between a tyre worn to 3mm and one worn to 1.6mm. That’s not a small margin. In heavy British rain, it can be the gap between stopping in time and not.
New tyres usually start with somewhere between 7mm and 9mm of tread, depending on the brand and whether they’re built for summer or winter use. From there, it’s all downhill.
The 20p Test Explained
This is the method most UK drivers reach for, and for good reason. It costs nothing and takes seconds.
Take a 20p coin and push it into the main tread grooves, which are the deepest, most continuous channels running around the tyre. Then look at the outer band on the edge of the coin. If the rubber covers that band, your tread is above 1.6mm and legal. If the band stays visible, the tyre may be below the limit and you should get it checked by a professional straight away.
Don’t just test one spot. Tyres wear unevenly, so check at three or four points around the circumference and across the width. Honestly, the whole thing takes longer to explain than to do. Knowing how to handle a sudden flat tyre at home is useful too, but spotting worn tread early means you rarely get that far.
Using a Tread Depth Gauge
The 20p test tells you whether you’ve passed or failed. It won’t tell you that you’re sitting at 2.1mm and need to plan ahead. For that, you want a tread depth gauge.
These are cheap, often under a fiver, and dead simple. Place the probe into the deepest part of a main groove, press the base flat against the tread, and read off the measurement. Take readings at the inner edge, the centre, and the outer edge of each tyre. Recording those numbers does two things. It shows your exact margin, and it reveals uneven wear that a coin would miss.
If you’d rather skip the DIY route, professional home tyre fitting includes a proper inspection as standard, so the tyres get measured properly while any work is done.
Tread Wear Indicators: The Built-In Check
Here’s something a lot of drivers walk past every day without noticing. Most modern tyres have tread wear indicators moulded into them. They’re small raised bars of rubber sitting inside the grooves, set at exactly 1.6mm.
When the surrounding tread wears down level with those bars, the tyre has reached the legal limit. Simple as that. Look for a small “TWI” marking, or a similar symbol, stamped on the sidewall to find where the bars sit. Pirelli notes these indicators usually appear every 60 degrees around the tyre, so you’ve got several reference points to work from.
It’s worth saying the bars only show you the legal floor. By the time the tread is flush with them, you’ve long passed the point experts would have replaced the tyre.
What Different Wear Patterns Tell You
A tyre that wears evenly is doing well. One that doesn’t is trying to tell you something. Reading these patterns at home can save you from a much bigger repair bill later.
| Wear Pattern | Likely Cause | What To Do |
| Centre worn faster than edges | Overinflation | Check and correct tyre pressure |
| Both edges worn, centre fine | Underinflation or slow puncture | Check pressure, inspect for leaks |
| One inner edge worn heavily | Wheel alignment or worn suspension | Book an alignment check |
| One outer edge worn heavily | Alignment, or hard cornering | Alignment check, ease off bends |
| Cupping or scalloped dips | Unbalanced wheels or worn dampers | Wheel balancing or suspension check |
Inner edge wear deserves a special mention. It’s a common MOT failure and it hides well, because the inside of the tyre is the part you never really look at. Turn your steering wheel fully to one side and you can see it properly. If one edge is noticeably balder than the rest, the tyre might still pass the central 1.6mm check but the underlying alignment fault won’t fix itself.
How Often Should You Check?
There’s no single rule, but a useful habit is once a month, plus before any long journey. TyreSafe and most tyre retailers suggest roughly that frequency. Two minutes a month is hardly demanding.
A few extra pointers worth keeping in mind:
- Check tyres when they’re cold, ideally before driving or at least three hours after.
- Park on level ground with the handbrake on.
- Use a torch if light is poor, since shallow grooves are easy to misjudge.
- Don’t forget the spare, if your car still carries a full-size one.
If you keep finding yourself topping up pressure between checks, that’s a sign of a slow leak. Understanding what causes slow punctures helps you catch the problem before it drags your tread down with it.
When Checking Turns Into Replacing
So you’ve done the check and the news isn’t great. What now?
Legally, the line is 1.6mm. But the legal limit and the sensible limit aren’t the same thing. The RAC, TyreSafe and the Royal Society for the Prevention of Accidents all point to 3mm as the practical replacement threshold, because braking performance drops off sharply below that. Waiting until 1.6mm is cutting it fine, and a single hard emergency stop can shave off a surprising amount of tread.
The penalties make the case on their own. Each illegal tyre can cost up to £2,500 and 3 penalty points. Four bad tyres and you’re looking at a potential £10,000 and a ban. There’s also the insurance angle, which drivers tend to overlook: an accident on illegal tyres can give your insurer grounds to refuse a payout.
If a tyre is past it, deciding when to replace tyres instead of repairing them comes down to wear, damage location and age. Worn-out tread isn’t repairable. That one always means a new tyre. You can read the official guidance on the RAC’s tyre tread advice page for the legal detail.
A Final Word
Checking tread depth is genuinely one of the easiest pieces of car maintenance there is. No tools, no mess, no expertise required. Keep a 20p in the door pocket and make it a monthly thing, the same way you’d glance at your fuel gauge.
The real value isn’t passing the MOT, though that helps. It’s knowing your car will actually stop when a wet roundabout in February asks it to. That’s worth two minutes of anyone’s time.