When is a tyre illegal in the UK?
A tyre becomes illegal when its tread wears below the legal minimum, when it is damaged, or when it is run at the wrong pressure to the point of being unsafe. The headline number to remember is 1.6mm. For cars, the tread must be at least 1.6mm deep across the central three-quarters (the middle 75%) of the tread breadth, and right around the complete circumference of the tyre.
If any part of that central band drops below 1.6mm, the tyre is illegal to drive on and it will fail an MOT.
The 20p test
You do not need special tools to get a rough idea of where you stand. A 20p coin works well:
- Push a 20p coin into one of the main tread grooves.
- If the outer band of the coin is hidden by the tread, you are likely above the limit.
- If you can see the outer band, the tread is low — get the tyre checked properly with a gauge.
Check several points across the width of each tyre and around it, not just one spot. Tyres often wear unevenly, so one healthy reading does not mean the whole tyre is legal.
Why correct pressure matters
Tread is only half the story. Running the wrong pressure quietly ruins tyres and makes the car less safe.
- Safety: under-inflated tyres reduce grip and lengthen braking distances, and they can overheat at speed.
- Wear: too little pressure wears the outer edges; too much wears the centre. Either way you bin a tyre early.
- Fuel: soft tyres create more rolling resistance, so you burn more fuel for the same journey.
Always set pressures to your vehicle’s recommended figures, not whatever was in there last. You will find them on a sticker inside the driver’s door pillar, behind the fuel filler flap, or in the handbook. If you are carrying a heavy load or a full car of passengers, most cars have a higher recommended pressure for that — use it.
The penalties for illegal tyres
This is where it gets expensive. Driving on an illegal tyre can mean a fine of up to £2,500 and 3 penalty points — and that is per tyre.
Get caught with all four below the limit and you are looking at potential points totalling 12 and the loss of your licence, on top of the fines. It is also an automatic MOT failure, so a bad tyre will stop the car passing regardless.
The honest takeaway: tyres are not the place to gamble. Replacing one worn tyre is far cheaper than the fine, and a lot cheaper than the consequences of a blow-out or a failed emergency stop.
How a mobile fitter helps
This is where The Tyre Soldier comes in. Matt and Keri run a mobile tyre fitting service from Dundee (DD5), covering Tayside, Perthshire — including Highland Perthshire up to Pitlochry — and Fife. As a rough guide, that is within about 25 miles of Perth, Pitlochry or Dundee.
Rather than queueing at a depot, we come to you — at home, at work, or at the roadside:
- We can check tread and pressures and tell you honestly what needs doing.
- Any brand or budget, fitted on your driveway or in the work car park.
- One all-in price agreed before we set off — no surprises.
- Wheel balancing is included when we fit.
We are available 24/7. If a tyre has gone, or you have just failed the 20p test, call or WhatsApp 07449 206 581 and we will sort it. You can also get a quote online, read more about mobile tyre fitting, or see how fitting at your location works.