What Things Can Make Your Tyres Illegal?

Your tyres may feel fine while cruising on a sunny day, but you may be driving using illegal tyres! It’s important to know how to check your tyres and what to look out for so that you’re never caught out – for both safety and legality.

So what can make a tyre fall short of the legal requirements?

1. Low Tread Depth

One of the most regular problems that people face with their tyres is letting the tread depth get too low. The legal minimum is a depth of 1.6mm across the central three-quarters of the tyre’s face, and around the entire circumference.

You can read in detail about tyre tread patterns and tyre types here but, in short, the tread pattern of a tyre is developed to channel water and small debris away from your tyres, and let you maintain a firm grip on the road. The water can fill into the grooves of the pattern while the other parts of the tyre remain in contact with the ground.

When the tyres have worn too low, they won’t be able to channel the water and therefore won’t be able to maintain contact with the road.

Now, even though the legal minimum is 1.6mm, it’s worth changing your tyres when they’re around a depth of 3mm. This is because, typically, puddles on a road are likely to be deeper than 1.6mm.

2. Excessive tyre wear or sidewall damage

As important as keeping an eye on the tyre tread depth is for driving in wet weather, it’s also important for the sake of the stability of the tyre. Excessive wear can lead to weak spots in the tyre which, in turn, can lead to tyre blowouts.

When you’re driving at higher speeds, these can be fatal.

And it’s not just a case of hitting a big bump, because when you have excessively worn tyres, small, slightly sharp stones can burst your tyres too.

As such, it’s worth keeping in mind what condition your tyres are in. Inspect them regularly for any signs of cracking, bulging, or any damage to the sidewall. Damage to the sidewall means that a tyre is more likely to split, additionally, any bulging indicates a serious issue as it could be a sign of damage to the tyre structure. So have your tyres checked immediately if you see any bulging.

3. Mixing tyre ply

Tyres are made out of different rubber compounds for elasticity and strength, but on its own, most rubber can’t withstand the forces of internal pressure as well as those needed to hold a car up.

To stand up to these forces, and to give tyres specific characteristics, manufacturers mould the rubber around a layered lattice of cord. This cord grid acts as a flexible skeleton to hold the rubber together.

The different ways this chord grid is overlaid is what we call the tyre’s ‘ply’. There’s the base layer and the ‘crown’ layer above it. The way these are orientated is either known as “Radial Ply” or “Bias Ply”. This video from Michelin explains perfectly what the pros and cons of each ply are.

Importantly, primarily because they have different inherent characteristics, mixing different-ply tyres on your vehicle is against the law in the UK because they’ll handle the load differently than they should.

4. Under or over inflated tyres

Under-inflated tyres are the most common problem that drivers face – but you can actually receive a serious fine and points on your licence for driving with under-inflated tyres. The same is true for over-inflated tyres but for the opposite reasons.

With under-inflated tyres, they grip the road much more than they’re intended to and are less responsive to directional changes, which reduces your handling when going around bends or driving at higher speeds.

Overinflated tyres, on the other hand, could lead to blowouts and skidding. The more pressurised a tyre is, the less it’s able to grip a road, so the more likely your tyres spin or skid when braking.

5. Improper tyres for the vehicle’s use

This last point is the least common, but driving with tyres that are unfit for a vehicle’s purpose can be illegal. This usually applies to having tyres that don’t meet the load requirements of the vehicle or have a max speed rating that is unsuitable for the vehicle.

For example, fitting car tyres to a motorhome (which you’d really have to try to succeed in doing) is a bad idea, not only because they tend to be a smaller diameter, but because they can’t handle the weight of a motorhome. Vice versa, wheels that are too large for a vehicle will significantly affect handling and are likely to be dangerous without serious vehicle modifications – which themselves could render your vehicle illegal.

Worried about your tyres?

If you notice any excessive wear on your tyres, get them checked by an expert immediately by calling your local Kwik Fit centre.