What Makes Your Tyres Illegal?

26 February 2025

Are you sure your tyres are safe? Worn-out tyres can cost you more than just money - they can put your life at risk and lead to hefty fines. Many drivers overlook the warning signs that their tyres are no longer legal. In this blog, we’ll tell you all you need to know to keep your tyres safe and legal.

What is a legal car tyre ?

• Adequate Tread Depth: The legal minimum tread depth is 1.6mm across the central three-quarters of the tyre.
• Structural Integrity: A tyre must not have significant cuts, bulges, or cracking that compromises its strength.
• Proper Fitment and Certification: It should be the right size and type for your vehicle, bearing the appropriate markings and certifications (like the E-mark) that confirm it meets EU and UK safety standards

Many drivers are usually surprised to learn that even subtle issues that are often overlooked as mere “wear and tear”—can make a tyre illegal.

What makes your tyres illegal?

• Tread Wear Beyond the Limit: Once the tread depth drops below 1.6mm, you’re driving on tyres that are, by law, illegal. This is enforced to ensure your vehicle maintains proper grip and handling.
• Hidden Damage: Small cracks, uneven wear patterns, and even minor sidewall damage can evolve into serious safety hazards. These issues can weaken the tyre so they can lose pressure quickly or could ‘blow out’ if you drive over uneven surfaces.
• Improper Tyre Type or Mismatch: Using tyres that aren’t designed for your vehicle or the current weather conditions can also be a violation. This is often overlooked until a professional inspection, or an unexpected police check, brings it to light (don’t let it be you!).

What does an illegal tyre look like?

• Bald Tread Areas: Even if just a portion of the tread is worn down to the wear indicators (or below 1.6mm), your tyre would be considered illegal. This isn’t always visually obvious so you should check your tyre tread every few weeks.
• Subtle Damage: Look for small cracks in the rubber, slight bulges along the sidewall, or an irregular wear pattern. These can be early indicators of underlying damage.
• Inconsistent Wear: Sometimes a tyre will show signs of uneven wear due to misalignment, fitting tyres without paying attention to the directional tread, or improper inflation.

Knowing these subtle differences is crucial. It’s not enough to say a tyre “looks okay” - you need to be aware of the small details that could make it illegal.

How to test if you have legal tyres

• The 20p Coin Test:
  Insert a 20p coin into the tread groove. If you can see any part of the coin’s edge, it’s a clear sign that your tyre’s tread depth is below the required 1.6mm. This isn’t just a rule of thumb, it’s an easy-to-remember method to identify potential worn illegal tyres.
• Detailed Visual Inspection:
  Rather than just a quick glance, examine the entire tyre surface. Look for areas where the tread has worn unevenly or where small cracks and bulges are developing.
• Professional Tread Depth Gauge:
  For a more precise measurement, invest in a digital tread depth gauge. While the coin test is a great start, a gauge will give you an exact reading, ensuring you’re not unknowingly driving with illegal tyres.

This combination of tests helps you identify the subtle issues that generic advice might overlook.

Understanding these outcomes underlines why it’s vital to regularly check your tyres using our what makes your tyres illegal theory test.

How long do tyres last?

Tyre longevity isn’t set in stone, it depends on how you drive and the conditions you face.

• Mileage and Age: Most tyres are designed to last around 40,000 to 50,000 miles, but this can be significantly reduced if you drive frequently in harsh conditions or neglect regular maintenance.
• Environmental Conditions: UK roads, with their mix of wet weather and occasional heatwaves, can accelerate tyre degradation.
• Driving Habits: Aggressive driving and improper inflation can increase wear, meaning your tyres might become illegal sooner than expected.

Staying proactive with your tyre maintenance ensures that you’re not caught off guard when those subtle signs of wear start to appear.

What is the legal limit for tyres?

In the UK, the legal threshold for tyre tread is clear: you must have at least 1.6mm of tread depth measured across the central three-quarters of the tyre. This standard isn’t just for aesthetics - it’s a critical safety measure designed to ensure proper road grip and handling.

• Routine Checks: Regularly perform the 20p coin test and a thorough visual inspection to ensure your tyres remain above this limit.
• Compare and Contrast: Familiarise yourself with illegal tyres examples and worn tyres illegal tyres examples so you know exactly what to look for.
• Stay Informed: Tyre technology and safety regulations can evolve. Keep up to date with any changes in the law to ensure your vehicle always complies.

Meeting this standard isn’t just a legal obligation—it’s an investment in your safety and that of everyone on the road.