What makes your tyres illegal? UK law, tread depth & penalties

At a glance:

• The criteria: In the UK, a tyre becomes illegal if it has a tread depth below 1.6 mm, visible structural damage (bulges, cuts, exposed cords), incorrect inflation, or incorrect type/speed ratings for the vehicle.
• The penalties: Consequences are severe, reaching up to £2,500 and 3 penalty points per defective tyre. Accumulating four illegal tyres can result in 12 points and an automatic driving ban.
• The risks: Illegal tyres trigger automatic MOT failures, and insurers can completely reject accident claims if defective rubber contributed to the incident.

The information in this guide is intended as general advice. For vehicle-specific queries, always consult your local Point S tyre professional or your vehicle handbook.

What are the UK legal requirements for tyres?

In the UK, the Road Vehicles (Construction and Use) Regulations 1986 set the legal framework determining whether your tyres are roadworthy. These regulations lay out precise standards every vehicle must meet to remain compliant and safe on public roads.

To be considered fully legal, a tyre must meet the following criteria:

1. Minimum tread depth: Must be at least 1.6 mm across the central three-quarters of the tread width, running continuously around the entire circumference.
2. Structural integrity: Must be entirely free from deep cuts, bulges, embedded objects, or exposed internal cords.
3. Correct inflation: Operating pressures must match manufacturer specifications; severe over- or under-inflation compromises safety.
4. Matching types: Tyres on the same axle must match in structure (mixing radial and cross-ply designs on one axle is strictly illegal). Your tyres must carry the correct speed and load ratings specified by your vehicle manufacturer. Learn more about how to read your tyre markings.
5. Approved markings: Every tyre must feature a moulded approval safety mark on the sidewall—either a legacy EU 'e' mark or the post-Brexit Great Britain type-approval marking.

What makes your tyres illegal?

Several common maintenance oversights and driving habits can render your tyres illegal. Understanding these factors helps protect your driving licence, your wallet, and your safety.

Insufficient tread below the 1.6 mm limit

While 1.6 mm is the absolute legal boundary, tyre professionals strongly recommend replacing tyres once they wear down to 3 mm for wet-weather safety.

Tests conducted by the Motor Industry Research Association (MIRA) show that cars braking on wet roads at 1.6 mm tread experience up to 44% longer braking distances than those stopping at 3 mm. When tread depth drops too low, the tyre loses its ability to clear water from the road surface, dramatically increasing the risk of aquaplaning and complete loss of control.

Cuts, bulges, and sidewall damage

Visible damage to a tyre's sidewall renders it defective and illegal immediately, regardless of how much tread depth remains.

• Sidewall bulges: A bulge or bubble indicates that the internal structural carcass ply has ruptured behind the rubber. The tyre is highly susceptible to a sudden blowout, particularly at high speeds.
• Cuts and gashes: Deep slices caused by glass, sharp stones, or debris can expose the underlying cord structure. If the fabric layer beneath the rubber is visible, the tyre is illegal.

Potholes and kerb strikes are the leading causes of hidden sidewall damage on UK roads. Severe impacts can crush the tyre carcass against the wheel rim, damaging the inner liner out of normal sight

Dangerous over- or under-inflation

Driving with severely incorrect tyre pressures breaches Regulation 27 of the Road Vehicles Regulations. Maintaining the correct pressure is critical for three core reasons:

• Safety: Under-inflated tyres flex excessively and overheat, risking a blowout; over-inflated tyres reduce the footprint on the road, compromising cornering grip.
• Economy: Incorrect pressures cause rapid, uneven tread wear, significantly shortening tyre life.
• Environment: Low tyre pressures increase rolling resistance, raising fuel consumption and carbon emissions.

Under-inflation causes the tread to wear excessively on the outer edges, dulling your steering response. Over-inflation forces the centre of the tread to bear the entire vehicle weight, wearing out the middle section prematurely.

Mixing radial and cross-ply tyres

It is illegal to mix radial and cross-ply tyres across the same axle because they behave fundamentally differently under load.

Cross-ply tyres use diagonally overlapped plies to create a rigid structure, whereas radial tyres arrange plies perpendicular to the direction of travel for reduced heat and better modern grip. Radial tyres are easily identified by the 'R' marking on the sidewall (e.g., 205/55R16). Aside from certain classic or vintage vehicles, almost all modern cars rely exclusively on radial tyres.

How to tell if your tyres are illegal

Conducting a quick monthly inspection takes only five minutes and can prevent a costly roadside penalty. Always check your tyres when they are cold; driving generates heat, which expands the air inside and produces falsely elevated pressure readings.

Tyre compliance checklist:

• Visual check > Pass: No cuts, cracks, or bulges. No exposed cords.
• 20p coin test > Pass: Outer band is fully hidden in main grooves.
• Pressure gauge > Pass: Level matches vehicle handbook specifications.

The visual inspection

Walk around your vehicle and check the entire visible surface of each tyre. Look closely for bulges, deep cracks from age, or embedded objects like nails or screws. Inspect the inner and outer sidewalls for signs of scuffing, tearing, or uneven edge wear that might indicate alignment problems.

The 20p coin test

The 20p coin method is a quick way to gauge tread depth without specialized tools. Insert a 20p coin into the main central tread grooves.

• If the outer band of the coin is completely obscured, your tread is above the 1.6 mm legal minimum.
• If the outer band remains visible, your tyre may be illegal and requires immediate measurement with a calibrated gauge.

Repeat this check at three distinct points around the circumference of each tyre, as uneven alignment can cause one section of a tyre to bald faster than the rest. For more detailed guidance, read our guide on checking tyre wear and tread depth.

Tyre wear indicators (TWI)

Modern tyres feature built-in Tyre Wear Indicators—small, raised rubber bars moulded into the base of the main tread grooves at exactly 1.6 mm.

You can locate them by looking for a small arrow or the letters 'TWI' on the upper sidewall. When the outer tread wears down level with these raised bars, the tyre has hit the legal limit and must be replaced immediately. MOT testers check these indicators during standard inspections.

Monitoring your TPMS

Cars first used on or after 1 January 2012 feature an automated Tyre Pressure Monitoring System (TPMS) that illuminates a dashboard icon if pressure drops significantly. While a helpful warning tool, note that a malfunctioning TPMS system itself (such as a faulty sensor illuminating the warning lamp) is classified as a major MOT failure, meaning the system must be fully operational to pass.

What are the penalties under UK tyre law?

The legal and financial consequences of driving on defective tyres are severe.

Roadside fixed penalties begin at £100 and 3 penalty points per illegal tyre. However, police officers hold the discretion to escalate serious or multiple defects to court prosecution rather than issuing a standard fixed notice.

In court, a magistrate can enforce the maximum statutory fines and apply cumulative points up to an automatic driving ban.

Tyre penalty summary table

Note: For goods vehicles or passenger vehicles adapted to carry more than eight passengers, the maximum statutory fine rises to £5,000 per tyre.

Enforcement outcomes at a roadside stop

If stopped by the police or a DVSA examiner, the severity of the tyre defect determines the legal outcome:

• Fixed penalty notice (FPN): Issued at the roadside for standard offenses, applying the baseline fine and points. In Scotland, this is processed as a Conditional Offer Notice.
• Court prosecution: Triggered if multiple illegal tyres are found or if the vehicle's condition is deemed explicitly dangerous to public safety.
• Prohibition notice: Issued immediately for highly dangerous tyres. This legally bars you from driving the car away from the scene. The vehicle must remain stationary until a mobile fitter or recovery service replaces the offending tyres.

MOT and insurance implications

Defective tyres trigger an automatic MOT failure. Driving a vehicle to a testing centre with known illegal tyres remains an offence, making proactive checks vital before booking your test.

Furthermore, driving on illegal tyres carries an immense insurance risk. If you are involved in an accident and your insurer determines that defective tyres contributed to the collision, they can void your policy entirely. You will be left personally liable for all third-party injury claims, vehicle damage, and legal costs.

Book a free tyre check at your nearest Point S centre

If you are unsure about the condition or legality of your tyres, Point S has you covered. Our trusted network of over 400 independent fitting centres across the UK is standing by to keep you safe and compliant.

We offer completely free tyre safety checks, including precise tread depth measurements, cold pressure assessments, and a thorough inspection for hidden sidewall damage. Finding your local Point S centre and booking your slot online takes less than two minutes.

Frequently asked questions

Are part-worn tyres legal to buy in the UK?

Yes, but they must strictly comply with the Motor Vehicle Tyres (Safety) Regulations 1994. To be sold legally, a part-worn tyre must have at least 2 mm of tread depth across its width, be free of internal structural cuts or bulges, and carry a permanent, prominent "PART-WORN" stamp moulded into the sidewall in text at least 4 mm high.

Do motorcycle tyres have different legal requirements?

Yes. Motorcycles over 50cc require a minimum tread depth of 1 mm across the central three-quarters of the tread width. For mopeds and light bikes under 50cc, the original tread pattern must simply be visible. The rules regarding structural integrity, pressure safety, and load ratings remain identical to cars.

Is a tyre illegal if it is only worn bald on the very edge?

A tyre is illegal if any part of the tread within the central three-quarters width drops below 1.6 mm. If the extreme outer shoulder is worn flat but the central legal zone is above 1.6 mm, it may technically pass, but extreme edge wear usually points to severe tracking or inflation issues. It should be inspected immediately before it spreads into the regulated zone.

Can I legally drive my car directly to a garage if my tyres are illegal?

No. The law makes no legal exception for driving to a garage to fix a tyre defect. If stopped by the police en route, you can still face points and fines. The safest, legal method is to call a mobile tyre-fitting provider or contact your local Point S centre to arrange a safe vehicle collection.

How long can I expect 5 mm of tyre tread to last?

On average, 5 mm of remaining tread provides roughly 15,000 to 20,000 miles of motoring. However, longevity depends entirely on your vehicle type, wheel alignment accuracy, and individual driving style. Frequent harsh braking or urban stop-start driving will deplete this remaining tread much faster.