Your tyres are the only part of the car that actually touches the road. Everything you do — steering, braking, accelerating — happens through four contact patches roughly the size of your hand. If the rubber on those patches is worn, none of it works as well, and you often won't feel the difference until the moment you need grip most.
In Great Britain there is a clear legal minimum for how much tread a car tyre must have, and checking it takes about a minute with a coin you probably have in your pocket. It's the kind of quick habit that keeps you legal, keeps you safe, and shows up in theory-test questions about vehicle safety.
This guide covers the legal limit, the simple 20p test, why tread matters so much in the wet, and the penalties for driving on illegal tyres — all in plain English so it actually sticks.
Study time
26 min
Level
Core
Confidence
+10%
Practice
16 Qs
What you'll be able to do
- Understand a quick routine to check your car is safe before you drive — and an easy way to remember it.
- Understand how to tell if your tyres and brakes are safe — including a coin trick anyone can do.
- Understand what your warning lights mean by their colour — and how smooth driving saves your car and your fuel.
The facts that matter
- The legal minimum tread depth for cars is 1.6mm
- It must be at least 1.6mm across the central three-quarters of the tyre and all the way round
- The 20p test: if the coin's outer band is hidden in the groove, you're probably legal
- Tread clears water — worn tyres badly increase wet stopping distances and aquaplaning risk
- You can get points and a fine for EACH illegal tyre, and it's your legal responsibility
Make it stick
Memory anchors
One-point-six, all the way round
Picture the number 1.6 stamped around the whole circumference of the tyre and across its middle three-quarters. Not just one worn patch — the limit applies to the central band, right around.
Coin in, band hidden = fine
Slide a 20p into the main grooves. If the raised outer rim of the coin disappears, there's enough tread. If you can still see that band, the tyre may be below the limit — get it checked.
Tread is a water pump
Grooves exist to scoop rain out from under the tyre so the rubber can still grip. Bald tyre, nowhere for the water to go, and you're floating instead of gripping.
Stay sharp
The mistakes everyone makes
Checking only one spot
Tyres wear unevenly — often more on the inside edge or in the centre. Check the tread in several places around each tyre and across its width, not just the bit you can see easily.
Waiting until exactly 1.6mm
1.6mm is the legal floor, not the safe target. Wet grip drops off well before that, so many drivers replace tyres at around 3mm to keep proper stopping performance. Legal and safe aren't the same number.
Forgetting pressure, cuts and bulges
Tread depth is only part of the check. Tyres also need the correct pressure for the load you're carrying, and you should look for cuts, bulges and nails or stones lodged in the rubber.
Out on the road
What this looks like in real life
The rainy roundabout
Same driver, same speed, same puddle. On fresh tyres the car tucks in and grips; on tyres worn near the limit the steering goes light and vague as water builds under them. Tread is the whole difference on a wet approach.
The four-times fine
A driver stopped with all four tyres below 1.6mm doesn't get one penalty — it's points and a fine per tyre. That can mean enough points to lose a new licence, on top of the repair bill.
Go deeper
Lessons on this topic
Quick answers
Frequently asked questions
What is the legal tyre tread depth in the UK?
For cars, the minimum legal tread depth is 1.6mm. It must be at least that across the central three-quarters of the tyre's width and around its entire circumference.
How do I do the 20p test?
Put a 20p coin into the main grooves of the tyre. If the coin's outer band is hidden by the tread, you're probably above the legal limit. If you can see that band, the tread may be too low — have the tyre checked by a professional.
Why does tread depth matter so much?
Tread clears water from under the tyre so it can still grip in the wet. As tread wears down, wet stopping distances get much longer and the risk of aquaplaning — sliding on a film of water — goes up sharply.
What's the penalty for illegal tyres?
You can receive penalty points and a fine for each illegal tyre. With four bad tyres that adds up fast, and enough points can cost a new driver their licence. Keeping tyres legal is the driver's responsibility.
Should I wait until 1.6mm to change my tyres?
You don't have to, and many drivers don't. Grip in the wet fades before the legal limit, so replacing tyres at around 3mm is a common, safer habit. 1.6mm is simply the point below which they're illegal.
Turn tyre tread depth into marks
Reading builds understanding — practice makes it stick. Pick up where this guide leaves off, free.
Revision checklist
0/5Tick each point once you can explain it without looking.