What makes tyres illegal?

Monday 16th August 2021

Illegal tyres

Ensuring your tyres are legal is an important part of vehicle maintenance. Some of this will be taken care of annually during your MOT test – but it’s important to understand how your tyres could be illegal, as this could lead to an MOT fail, or a hefty fine if you’re caught with illegal tyres on the road. So, how can you ensure your tyres are legal all year round?

What makes your tyres illegal?

1. Excessive tyre wear

Excessive or uneven tyre wear is a key component of what can constitute as an illegal tyre. This could refer to having large, deep cuts in the sidewall, for example, or having tyre wear in uneven places – leading to a dangerous tyre which isn’t meeting the specific safety requirements. Excessive tyre wear can also lead to weak spots in the tyre which then, in turn, may lead to a tyre blowout.

Inspecting your tyres regularly for any signs of uneven or excessive tyre wear is integral to ensuring your tyres are kept to a legal requirement – and be sure to keep an eye out for any bulging, cracking or damage to the sidewall, too. If you suspect any damage, you should book in to have your tyres checked immediately.

2. Tyre tread depth

Tyre tread is one of the most common causes of illegal tyres, and one that needs to be monitored carefully to avoid. Tyre tread refers to how thick the outer rubber of your tyre is – as there is a legal limit of 1.6mm in the UK, and if your tyre’s tread depth is below this, you could be due a large fine. However, it’s worth noting that a tyre tread depth of 3mm is enough to warrant a replacement tyre – so keep your eye on your tyre tread!

This could then eventually lead to bald tyres – which is when the rubber has totally worn down on the tyre, and is extremely dangerous for drivers. Learn how to check your tyre tread depth from our detailed guide to keep your tyres legal and safe.

3. Mixing tyres

There are often a lot of questions around whether or not you can mix your tyres. In most instances, mixing tyres is a big no-no, especially when you’re considering mixing seasonal tyres or mixing tyres on the same axle – so it’s important to be clued up to avoid accidental illegal tyres!

The tyres on your vehicle must all be fitted for the same season in mind, as winter tyres have extremely different characteristics to summer tyres – meaning if both were used on the same vehicle at the same time, they would counteract each other’s performance capabilities.

Mixing tyres on the same axle is equally as dangerous, if not more, and it is illegal to mix cross-ply and radial-ply tyres across the same axle. It’s advised the axle is fitted with identical tyres – as mixing tyres could lead to an imbalance on your vehicle, comprising both performance and safety.

4. Driving with tyres unfit for the vehicle

Although this is typically a less common example of an illegal tyre, driving with tyres which are not appropriate for the vehicle is still likely to land you with a hefty tyre fine. For example, driving a MINI cooper with tractor’s wheels is an extreme example – but one that is likely to compromise the safety and performance of the vehicle, meaning that they would be deemed as illegal tyres.

These types of illegal tyres are typically calculated based on if they meet the load requirements of the vehicle or not, or if they have a maximum speed rating which is unsuitable for the vehicle.

5. Incorrect tyre pressure

If your tyres are overinflated or underinflated, this can also lead them to becoming illegal. Tyre pressure is important because if your tyres are incorrectly inflated, this can cause serious damage to your tyres and the performance of your vehicle.

• Overinflated tyres – reduces the contact with the road surface, meaning skidding and tyre blowouts could be possible – with less grip on the road.
• Underinflated tyres – reduces the handling of your vehicle significantly due to an increased grip to the road surface, and a reduced response to directional changes.

Learn how to tell what pressure your tyres should be from our helpful guide.

Ensure your tyres are legal with Formula One Autocentres

Here at Formula One Autocentres, we offer regular car servicing and tyre checks from our team of experts. Locate your nearest centre today and book in for your next tyre check.