A guide to tyre tread law in the UK
heycar editorial team
- Make sure you stay the right side of the law when it comes to tyres
- What is the minimum legal tread depth?
- We explain runflat tyres
If there’s any part of our car that we completely take for granted, it’s probably the tyres. These four black round things are all that keeps our cars in contact with the road. To maximise driving safety it’s vital that they’re in good condition.
Here we answer the top 10 questions about car tyres.
When should tyre pressures be checked?
On most cars the contact patch between your car’s tyres and the road is approximately the same size as a postcard. Therefore, it makes sense that each is in tip-top condition. Safety experts recommend that you inspect your car’s tyres ideally once every two weeks and at least once a month. You should check the air pressure is correct, the tread depth is legal, and look for any other damage such as bulges or tears in your tyres’ sides. For more information on checking tyre pressure and inflating your tyres, please click here.
What is the minimum legal tread depth?
In the UK and other European countries, the legal minimum tyre tread depth is 1.6mm. However, tyre experts advise drivers to consider renewing their tyres when the tread is down to 3mm. The more worn your tyres are the harder it will be for the tyre to move water away, making it difficult for the tyres to find grip on the road. Wet grip is significantly reduced when the tread wears below 3mm.
How much tread does a new car tyre have?
A new car tyre tread depth is approximately 8mm. How quickly this wears down depends on several factors. Front tyres wear faster than those at the back because they have the weight of the engine over them and must cope with steering. Wear rate also depends on driving style and driving conditions.
Do you need to replace all four tyres at once?
No, you don’t. You can replace one tyre at a time, and you may need to if you get a puncture. Tyre makers always advise that new tyres are put on the rear. The newer the tyre is, the more grip it has. In general, it is easier to cope with front tyres skidding than the rear ones losing their grip. A rear slide can cause the car to spin, putting many at risk.
Can you repair a punctured tyre?
It’s entirely legal to mend a punctured car tyre. However, the repair must be in the central three quarters of the tread area. If you have a puncture in the side of the tyre – known as the sidewall – it can’t be repaired. The sidewall flexes when a car is cornering and any repairs in this area may fail suddenly and cause you to lose control.
What are the different types of tyre?
Most tyres fitted to cars in the UK are what’s known as summer tyres. The blend of chemicals that’s used to make the tyre and its tread pattern are best suited to the UK’s climate for most of the year.
When temperatures dip below 7 degrees Celsius, regular summer tyres become stiffer and less able to grip the road. That’s why some countries, such as Germany, require cars to have winter tyres fitted in the colder months. Winter tyres are made of specific materials and have a tread that’s designed to find grip on slippery surfaces such as ice and snow.
All-season tyres are a combination of the two and something that many tyre companies are now offering. These are usually winter tyres that include some properties of summer tyres.
As well as different tyres for different climates, there are also special tyres for various cars. Drivers of sports cars can buy high-performance tyres and fuel-conscious drivers can choose low rolling resistance tyres. These are designed to have less friction against the road’s surface for improved economy.
What do the letters and numbers on the side of a tyre mean?
You will notice quite a lot of writing on the side of your car’s tyre. As well as the manufacturer’s name, the most important are the tyre’s dimensions. You need to know these if you’re inflating your tyre of planning to replace it.
They will be displayed as 225/55 R16 91V, for example. The 225 is the width of the tyre in millimetres from sidewall to sidewall. The 55 is what’s called the aspect ratio or profile. That’s the height of the sidewall, expressed as a percentage of the tyre’s width.
The R16 shows R for radial (the construction of virtually all modern tyres) while 16 is the width in inches of wheel it will fit. The 91 is called the load index which is how much weight a tyre can bear, while the V is its speed rating. The later the letter in the alphabet, the faster the tyre is capable of going. For example, a tyre with the letter V would be able to go faster than a tyre with the letter L. Your car’s user manual will tell you the load and tyre speed ratings for your car in the UK.
How does tyre labelling work?
When you buy tyres, they now have a label. This rates each tyre over three areas of performance: economy, wet grip, and exterior noise. Economy is measured from A (the best) to G, so you can gauge the potential savings of one tyre over another. Wet grip is again measured from A to G, which shows how safe a tyre is. And the exterior noise the tyre makes is shown in decibels.
Is there a maximum age limit for tyres?
There is no legal maximum age for a tyre. But the older a tyre gets, the more prone to failing it might become. Tyres are also vulnerable to UV sunlight rays, particularly if they’re not used much. This can cause the tyre’s sidewalls to crack.
You can find a tyre’s age by looking for the letters DOT on the sidewall. These will usually be followed by more seemingly random letters and then four numbers. Those numbers will be the week of the year followed by the year of manufacture. So, the number 4217 shows the tyre was made in the 42nd week of 2017.
What is a run-flat tyre?
Sometimes called a self-supporting run-flat or SSR tyre, these are tyres with a very stiff sidewall. Tyres usually rely on air to support the car that sits on them. Run-flats use the sidewall so even if the tyre is punctured it can still be driven on, although it must be replaced quickly.