What Makes Tyres Illegal?
FixMyCar explains what can make a tyre illegal and how to check yours.
Book a car repair nowEllie Dyer-Brown
Monday November 25 2024
7 min read
Driving on damaged, worn or incorrectly inflated tyres poses a serious safety risk. If you don’t monitor their condition, you could find yourself on the wrong side of the law. But what makes a tyre road-legal, and how can you check? Find out in this guide.
What are illegal tyres?
Tyres can last thousands of miles before they need replacing. While this is good news for your wallet, it also means it’s easy to forget about them, which could result in you driving on illegal tyres if you don’t notice they’re worn out.
To help you avoid the situation described above, let’s look at what can make a tyre illegal.
1. Tread depth
Tyre tread is made of grooves that channel water away from the tyre’s surface and the road, creating more grip. However, when the tread becomes too shallow, it loses its ability to remove water and debris. This compromise in performance can lead to longer stopping distances and a higher risk of skidding and aquaplaning.
The law says: Tyres must have a tread depth of at least 1.6 mm around the circumference.
2. Pressure
Tyre pressure affects the distribution of a vehicle’s weight and impacts the tyre’s ability to grip the road.
Overinflated tyres have a smaller contact area with the road, which increases the risk of skidding and blowouts.
Underinflated tyres have less traction and stability, so the response to your steering input is slower and less precise.
The law says: Tyres should be inflated according to the manufacturer’s recommendations.
3. Sidewall damage and/or significant wear
Damaged tyres or tyres with significant wear are often unstable and at greater risk of blowouts, which can cause major road accidents. The two main signs of damage to keep an eye out for are bulges and cracks.
If you spot a sidewall scratch or cut, it’s best to get it checked to make sure you’re not at risk of a blowout. Tyres with a cut larger than 25 mm or 10% of the section width are illegal.
Damaged or severely worn tyres will also result in an MOT failure. Read about other common MOT fails and how to avoid them.
The law says: There should be no visual damage on your tyres.
4. Mixed tyre ply
Car tyres are made of different rubber compounds designed for strength and elasticity, but this alone isn’t enough to support a car’s weight. Manufacturers mould the rubber around a latticed metal cord (known as ply) to solve this problem and give the tyre particular characteristics.
However, combining different ply tyres is illegal in the UK because they handle the vehicle’s load differently. Mixing them means your car won’t have a unified stress tolerance across all tyres, which puts you at increased risk of tyre damage and blowouts.
The law says: You must not mix tyres with different ply on the same axle.
5. Improper tyres for the vehicle’s use
It’s important that your tyres:
Meet the vehicle’s load requirement
Have a suitable maximum speed rating
Are the correct size
This guide explains how to choose the right tyres for your car.
The law says: Your tyres must meet the requirements of your vehicle.
Examples of illegal tyres
The images below show examples of illegal tyres.
Bald tyres
The tyre on the left is bald.
Bulging tyres
Damaged tyres
How will I know when to change car tyres?
You’ll usually be able to see visual signs when your tyres need replacing, such as bald patches, cracks and scratches.
Typically, you can expect front tyres to last up to 20,000 miles and rear tyres to last around 40,000 miles. As they come towards the end of their lifespan, you should check their tread regularly using a gauge or even a 20-pence piece.
Experts recommend changing tyres when they reach a depth of 3 mm to ensure you aren’t risking your safety in wet conditions, but the minimum legal depth is 1.6 mm.
You’ll know your tyres need replacing if you experience any of the following:
Increased or unexplained loss of tyre pressure
Worn tread
Cracks, slashes or bulges in the rubber
Steering wheel vibrations
How to test if you have legal tyres
Follow the steps below to find out whether your tyres are legal.
Suitability check. Look in your owner’s manual to find your car’s tyre specifications. Next, check your tyre labels to ensure they meet the requirements.
Visual inspection. Look for cracks, bulges, bald patches and any other signs of damage on each tyre.
Tread test. Use a tread gauge or 20-pence coin to see how much tread your tyres have. They need at least 1.6 mm around the entire circumference to be legal.
If your tyres pass all the above tests, they are legal. However, if they fail, you should replace them.
Did you know...
Over 6 million tyres in the UK are illegal, according to TyreSafe.
What will happen if I drive with illegal tyres?
You could face police action if you’re caught driving with tyres that don’t meet the legal requirements outlined above. Different actions may be taken depending on the circumstances:
Penalty notice - The police may issue a Fixed Penalty Notice (FPN), resulting in a fine and points on your licence. The number of points and size of the fine can vary based on the offence.
Vehicle impoundment - If your vehicle is linked to other legal issues or the tyre damage is particularly dangerous, the police may impound it until the necessary repairs are completed.
Prohibition notice - In severe cases, the police may issue a Prohibition Notice, which forbids you from driving the vehicle until the tyres are replaced.
Court proceedings - Repeat offences and serious cases can lead to prosecution in court, more penalty points, a substantial fine and a potential driving ban if you’re found guilty.
Police actions in response to illegal tyres can vary depending on the circumstances and discretion of the officer.
If you receive a penalty notice, the most likely outcome is that you will receive:
Three points on your licence
A fine of up to £2,500 per illegal tyre
An invalidated insurance policy
Learn about common driving offences and penalties.
Did you know...
On average, 159 people are killed or seriously injured from defective tyre accidents each year in the UK, according to TyreSafe.
Replacing illegal tyres
Illegal tyres pose a genuine safety risk and should be replaced as soon as possible. If you need help choosing your next set, check out our ultimate car tyres guide for buying tips, advice and recommendations.
Frequently asked questions
You can get points on your driving licence if caught with illegal tyres. You may also get a fine and, in extreme cases, a driving ban.
Cracked tyres can be illegal, depending on the size of the damage. A cut larger than 25 mm or 10% of the tyre's section width is deemed illegal.
Old tyres aren’t automatically illegal. Their age is less important than their condition - if they have plenty of tread and aren’t damaged or excessively worn, they are OK to use.
Perished tyres are illegal in the UK because their strength and structure is compromised, presenting a safety risk.
Stretched tyres aren’t necessarily illegal, but they will make your car fail its MOT.
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- Car Ownership
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Ellie is FixMyCar's Content Manager. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers that is easy understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.