Tyre Failures and the MOT Test

The MOT test is a crucial annual inspection designed to ensure your vehicle is safe and roadworthy. While many drivers focus on the engine, brakes, and lights, the condition of your tyres plays a significant role in passing this vital examination. Indeed, tyres are one of the most common reasons for a vehicle to fail its MOT. Understanding what the testers are looking for and the legal requirements can save you time, money, and potential heartache.

Tyre Tread Depth: The Legal Minimum

One of the most fundamental aspects of tyre safety, and a primary concern for MOT testers, is the tread depth. The legal minimum tread depth for cars in the UK is 1.6mm across the central three-quarters of the tyre's width, around its entire circumference. Any less than this, and your vehicle will fail its MOT. Testers will use a tread depth gauge to accurately measure this. It's not just about avoiding an MOT failure; driving with worn tyres significantly reduces grip, especially in wet conditions, increasing the risk of aquaplaning and accidents.

Why is Tread Depth So Important?

The grooves in your tyre tread are designed to channel water away from the contact patch between the tyre and the road. As the tread wears down, these grooves become shallower, making it harder for the tyre to disperse water. This leads to a loss of traction and a much longer braking distance. In the UK, with our frequent rainfall, this is a critical safety feature.

Tyre Condition: Beyond the Tread

While tread depth is paramount, it's not the only tyre-related issue that can lead to an MOT failure. Testers will also meticulously inspect the overall condition of the tyre for various forms of damage and deterioration.

Common Tyre Defects to Watch For:

• Cuts and Cracks: Any cuts or cracks that are deep enough to expose the ply casing or are longer than 25mm will result in a failure. These can compromise the structural integrity of the tyre.
• Bulges and Blisters: These indicate internal damage to the tyre's structure, often caused by impact. A bulge or blister is a serious safety hazard as it suggests the tyre could fail catastrophically.
• Perished Rubber: Over time, rubber can degrade, becoming hard, brittle, and prone to cracking. Perished tyres, often a sign of age or exposure to harsh conditions, can also lead to a fail.
• Underlying Structure Damage: This can include damage to the sidewall or any signs that the tyre's internal structure has been compromised.

Tyre Size and Type: Matching Your Vehicle

It might seem obvious, but ensuring your tyres are the correct size and type for your vehicle is also a requirement. The MOT manual specifies that tyres must be of a type and size appropriate for the vehicle, as specified by the manufacturer. This means:

• Correct Size: Using tyres that are too small or too large can affect handling, braking, and speedometer accuracy.
• Correct Type: While not always a fail unless it's a clear mismatch, using tyres not suitable for the vehicle's intended use (e.g., racing slicks on a family car) could be noted. Importantly, if a vehicle is fitted with different types of tyres (e.g., a budget brand on one side and a premium brand on the other), this can be a reason for failure if they are fitted incorrectly.

Tyre Matching: A Crucial Detail

A common area of confusion and a frequent cause of MOT failure relates to tyre matching. The rules state that tyres on the same axle must be of the same make, model, and size. Furthermore, they should ideally have a similar tread pattern and wear characteristics. While having different tyres on the front and rear axles is generally acceptable, mixing makes or tread patterns on the same axle is a definite no-no for the MOT. This is because different tyres can have varying grip levels and braking performance, leading to unpredictable handling.

Tyre Pressure: A Subtle but Important Factor

While an MOT tester won't typically check your tyre pressures directly, incorrect tyre pressure can lead to uneven tyre wear, which will be inspected. Under-inflated tyres wear more on the outer edges, while over-inflated tyres wear excessively in the centre. Both scenarios can lead to the tread depth falling below the legal limit in specific areas, resulting in a fail.

Maintaining Optimal Tyre Pressure

It's good practice to check your tyre pressures regularly, at least once a month and before long journeys. The recommended pressures for your vehicle can usually be found on a sticker inside the driver's door frame, in the owner's manual, or sometimes on the fuel filler flap. Using a reliable pressure gauge is essential.

Wheel Alignment and Balancing

Although not directly tested as part of the MOT, issues with wheel alignment and balancing can indirectly cause tyre wear that leads to a failure. If your steering wheel is pulling to one side, or you notice uneven wear patterns on your tyres, it's a strong indication that your alignment or balancing may be off. Addressing these issues proactively can prolong the life of your tyres and prevent MOT failures.

What Happens If Your Tyres Fail the MOT?

If your vehicle fails its MOT due to tyre issues, you will be issued with a 'Refusal of an MOT Test Certificate'. The specific reasons for the failure will be detailed. You will then need to have the necessary repairs or replacements carried out. You can continue to drive your vehicle if it is already taxed and the existing MOT certificate is still valid, but only to a pre-arranged appointment for the repair and re-test. However, if your MOT has expired, driving the vehicle is illegal, and you risk further penalties.

Pre-MOT Tyre Checks: Your Responsibility

The best approach is to be proactive. Before your MOT is due, conduct a thorough check of your tyres yourself. Look for:

• Tread Depth: Use a 20p coin. If you can see the outer band of the coin when placed in the deepest part of the tread, it's likely below 1.6mm and needs replacing.
• Sidewalls: Check for any cuts, bulges, or cracks.
• General Condition: Ensure there are no foreign objects embedded in the tread.
• Matching: Verify that tyres on the same axle are identical.

Summary Table: Tyre MOT Pass/Fail Criteria

Frequently Asked Questions (FAQs)

Q1: Can I pass the MOT with slightly less than 1.6mm tread if I only do short journeys?

A1: No. The legal minimum tread depth of 1.6mm is a strict requirement for all vehicles. Driving with less is illegal and will result in an MOT failure, regardless of your mileage.

Q2: What if my spare tyre has good tread?

A2: The MOT test only inspects the tyres fitted to the vehicle for normal use. The spare tyre is not tested unless it is fitted to the vehicle at the time of the test.

Q3: I have winter tyres fitted. Will they pass the MOT?

A3: Yes, provided they meet all the other legal requirements regarding tread depth, condition, and matching on the axle. Winter tyres are perfectly legal to use year-round in the UK, though they may wear faster in warmer temperatures.

Q4: My tyres are the correct size, but they are different brands. Will this fail the MOT?

A4: If the different brands are fitted to the same axle, then yes, this will cause an MOT failure. Tyres on the same axle must be of the same make, model, and size, and ideally have the same tread pattern.

Q5: Is it illegal to drive with tyres that have passed their expiry date?

A5: Tyres don't typically have an expiry date in the same way food does. However, rubber degrades over time. If a tyre shows signs of perishing, cracking, or significant age-related deterioration, it could fail an MOT and is also a safety risk.

In conclusion, tyres are a critical component of vehicle safety and a frequent reason for MOT failures. Regular checks of tread depth, condition, and ensuring correct fitment and matching are essential. By being aware of these requirements and performing your own pre-MOT checks, you can significantly increase your chances of a successful test and, more importantly, ensure your vehicle remains safe on the road.