Illegal Tyres: Examples Of What Can Make Your Tyres Unlawful

Are your tyres against the law? Choosing the right tyres for your car, properly maintaining the set you have, correctly inflating them, and replacing them when necessary are all wise practices – but it's also a matter of legality.

Certain factors can lead to your vehicle's tyres violating U.K. law. This, if left unaddressed, can lead to fines or more severe penalties. So, what makes a set of tyres unlawful?

Here are illegal tyres examples and how you can resolve them, so you can be safer (and more legally compliant) on the road:

1. Low Tread Depth

One of the most common road law violations is driving on tyres that are too thin. More specifically, the legal minimum for tread depth is 1.6 mm across the central three-quarters of the tyre's face, as well as around the entire circumference.

This depth is important, as it ensures the tread pattern can fulfil its purpose of:

• Channelling water and small debris away from your tyres
• Maintaining a stable grip on the road

When the tyre tread has an appropriate depth, water or debris can fill in the grooves of the pattern while the other parts of the tyre remain in contact with the ground. If the tyres have worn too thin, however, they can't channel the water or debris and will struggle to maintain contact with the road.

Likewise, the overall tyre becomes smooth, which limits the grip it can exert on the road. It will lack the necessary traction to safely hold on during turns, braking, or acceleration. This can lead to skidding, sliding, or poor handling.

Although the legal minimum is 1.6 mm, it's worth changing your tyres when they've reached a depth of around 3 mm. This will improve driving performance and limit damage to your suspension, but in more practical terms, puddles on a road are usually deeper than 1.6 mm. This makes rainy days hazardous for thin tyres.

2. Excessive Tyre Wear Or Sidewall Damage

Aside from tread depth, wear and tear across the entire structure of your tyre can make it legally unsafe. This is especially true for the sidewalls, as they bear the majority of your vehicle's weight.

Excessive wear can lead to weak spots, which, in turn, can result in blowouts. When you're driving at high speeds, this can be fatal. Even contact with small stones may trigger a rupture, and sidewall damage cannot be safely repaired.

As such, it's worth inspecting them regularly for any signs of cracking or bulging. Cracks indicate that a split is forthcoming, while a bulge indicates a serious issue with the tyre's structure.

3. Mixing Tyre Ply

Your tyres need to match each other in design and purpose. Mix-matching tyres incorrectly will put the vehicle, its handling, and the tyres themselves at risk of damage or loss of control. That's because of how a tyre's "ply" works.

Tyres are made of different rubber compounds to promote elasticity and strength. On its own, however, most rubber cannot handle the combination of internal pressure (from inflation) and outside force (from the weight of the car).

To withstand these elements - 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.

When overlaid in several different patterns, the cord grid is called the tyre's "ply." In general, there's a base layer and a "crown" layer above it. Based on their orientation, they are known either as "radial ply" or "bias ply."

Each is designed to hold the weight of a car (and any load it is carrying) in different ways. If you were to mix differently plied tyres on your vehicle, it would handle the load unevenly. This could lead to blowouts and poor steering, which could impact driving safety.

As such, this practice is against the law in the U.K. and no garage will condone or assist with it. If you were to mix the tyres yourself, it could result in fines.

4. Under Or Over Inflated Tyres

Consistently driving on under-inflated tyres can result in a serious fine or points on your licence. This is also true for over-inflated tyres, but for opposite reasons.

Under-inflated tyres are less responsive to directional changes, which reduces your handling on turns or when driving at higher speeds. They also place unnecessary weight on the sidewalls, which can damage the shape of your wheels.

Overinflated tyres, on the other hand, can lead to skidding. The more pressurised a tyre is, the less it's able to grip a road, which can result in a driver losing control. It can also damage the suspension over time.

Tyres may end up over- or under-inflated by accident, of course. Being caught with tyres in this state doesn't automatically mean a penalty. However, there may be consequences if they are in obviously poor condition or if they're routinely found in this state.

5. Improper Tyres For The Vehicle's Use

Driving with tyres that are unfit for a vehicle's purpose can be illegal. This usually applies to tyres that:

• Don't meet the load requirements of the vehicle
• Have a max speed rating that is unsuitable for the particular car

For example, fitting car tyres to a motorhome (which cannot be done easily) is unlawful. They will be unable to support the weight of a motorhome, and they are likely to result in either blowouts or lost control of the vehicle. This makes them knowingly unsafe on the road, which is illegal.

Vice versa, wheels that are too large for a vehicle can significantly affect handling or risk detaching without serious vehicle modifications (which, in and of themselves, could render your vehicle illegal).

Worried About Your Tyres?

If you're uncertain about the state of your tyres, or want to verify that you're in full compliance with U.K. road laws, reach out to our experts at Autofusion. We're happy to offer insight, advice, and servicing to ensure your tyres are in lawful shape and ready to keep you safe on the road.