Tyre Condition and Your Vehicle's MOT Test
Cracked tyres can be a significant concern when preparing for your vehicle's annual MOT test. Understanding the specific criteria used by testers is crucial to avoid an unexpected failure. An MOT test assesses various safety-critical components, and the condition of your tyres is paramount, not just for passing the test, but for your safety on the road.
The primary concern for an MOT tester regarding tyre cracks is whether the damage compromises the structural integrity of the tyre. Minor superficial cracking might be noted as an advisory, but significant or deep cracks, particularly those that penetrate the casing or expose the internal structure, will almost certainly lead to a failure. The MOT Testing Manual provides detailed guidelines that testers must follow, focusing on safety and roadworthiness.
- Cracked tyres can cause an MOT failure depending on the severity and location of the cracks.
- Testers assess if cracks compromise the tyre's structural integrity.
- Deep or extensive cracking, especially on sidewalls, is a common reason for failure.
- Minor superficial cracks may result in an advisory notice rather than an immediate failure.
It's vital to remember that the MOT is a snapshot of your vehicle's condition on a specific day. While a pass means it meets minimum safety standards, ongoing maintenance, especially for wear items like tyres, is essential. Proactive checks can save you time, money, and potential safety risks.
What Constitutes a Crack for MOT Purposes?
The MOT Testing Manual for Class 4 vehicles (which covers most cars) specifies that a tyre will fail if there is evidence of 'delamination or cracking of the tread structure, ply or sidewall'. This means inspectors are looking for more than just minor cosmetic ageing. They are specifically checking if the rubber has degraded to a point where it could lead to a catastrophic failure, such as a blowout. Cracks that are:
- Deep and penetrate into the tyre structure.
- Located on the sidewall, which is under constant flex and stress.
- Exposing the internal cords or casing of the tyre.
- Extensive and numerous across the tyre surface.
are all likely to result in a failure. The inspector will use their judgement, guided by the manual, to determine if the cracking presents a danger. A tyre with shallow, surface-level cracking that hasn't penetrated the rubber's integrity might be acceptable, but it could be flagged as an advisory for you to monitor or address later.
The Fair Test MOT Principle
The 'fair test' principle is central to the MOT system. It means the test should be applied consistently and fairly to all vehicles. For tyres, this translates to an objective assessment of their condition against the defined safety standards. A cracked tyre fails this test if the cracking indicates a risk to road safety. The AA MOT test, like any official MOT, adheres to these standards. It's not about the age of the tyre per se, but its condition. A brand-new tyre with a manufacturing defect causing a crack would fail, just as an older tyre that has degraded naturally would if the cracking meets the failure criteria.
Causes of Tyre Cracking
Why do tyres develop cracks, and what factors contribute to this degradation? Understanding the root causes can help you prevent premature wear and ensure your tyres remain in good condition for longer, significantly reducing the risk of an MOT failure.
Exposure to the Elements
The most common culprit behind tyre cracking is environmental exposure, particularly to UV (ultraviolet) light and ozone. These elements cause the rubber compounds in tyres to break down over time, leading to a loss of flexibility and the formation of surface cracks. Tyres that are frequently left stationary for long periods, especially in direct sunlight, are more susceptible. This is why vehicles stored for extended durations, or those used infrequently, might show signs of cracking even with ample tread depth remaining.
Chemical Exposure and Poor Maintenance
Contact with certain chemicals can accelerate rubber degradation. This includes aggressive cleaning agents, solvents, or even prolonged exposure to petroleum-based products. Furthermore, under-inflation or over-inflation can stress the tyre's structure unevenly, contributing to cracking. An under-inflated tyre flexes more than intended, generating heat and stressing the sidewalls, while an over-inflated tyre is more prone to damage from impacts and can develop cracks due to excessive rigidity.
Regularly clean your tyres with a mild, water-based cleaner and avoid harsh chemical solvents. If your car is stored, consider covering the tyres or using tyre protectors to shield them from UV and ozone.
Age and Deterioration
Tyres do not last forever, even if the tread appears adequate. The rubber compounds naturally degrade over time. Most manufacturers recommend replacing tyres that are older than six to ten years, regardless of tread depth, because the internal structure can become brittle and prone to cracking. The date of manufacture is usually stamped on the sidewall as a four-digit code (e.g., '3219' means the 32nd week of 2019). While a tyre might look visually sound, its chemical composition can change, leading to microscopic fissures that can develop into visible cracks.
Impact Damage and Stress
Sudden impacts, such as hitting a pothole or kerb at speed, can cause internal damage to the tyre structure, leading to cracks. Even without immediate visible damage, such impacts can weaken the tyre, making it more susceptible to cracking later. Driving with tyres that are not suited to the vehicle's load capacity or driving style can also introduce undue stress, potentially leading to premature degradation and cracking.
Identifying Tyre Cracks: What to Look For
How can you accurately identify tyre cracks that might pose a problem for your MOT test? Proactive visual inspections are your first line of defence. Becoming familiar with the typical patterns and locations of concerning cracks means you can address issues before they become critical failures.
Focus on the Sidewall
The sidewall of a tyre is particularly vulnerable to cracking. This area is constantly flexing as the tyre rotates and bears weight. Cracks here are often deeper and more concerning than those found on the tread surface. Look for any lines or fissures that run across the sidewall. If these cracks are more than a few millimetres deep, or if they appear to be spreading or widening, they are a strong indicator of potential failure. A cracked windscreen is another common MOT failure point, but for tyres, the sidewall is a key area of concern.
Tread Grooves and Edges
While the tread is designed to be durable, cracks can also appear between the tread blocks or along the edges where the tread meets the sidewall. These might be caused by age, chemical degradation, or stress from driving. If the cracks are deep enough to affect the tread's ability to grip the road or if they compromise the tyre's structural integrity, they will be flagged. Minor cracking on the very surface of the tread blocks might be acceptable, but anything more substantial warrants closer inspection.
It is essential to inspect your tyres regularly, not just when an MOT is approaching.
Checking for Delamination
Delamination refers to the separation of different layers within the tyre structure. This can manifest as bulging areas on the sidewall or tread, or cracks where the layers are starting to pull apart. Any sign of bubbling or separation is a serious safety concern and will undoubtedly lead to an MOT failure. This indicates a severe structural defect.
Tools for Inspection
You don't need complex equipment for a basic check. Ensure your vehicle is parked on a level surface, and turn the wheels to get a clear view of the inner and outer sidewalls. A good torch can be invaluable for illuminating cracks and assessing their depth. If you are unsure about the severity of any cracking, it is always best to consult a qualified tyre professional or your local garage. They can provide an expert opinion and advise on necessary actions.
When is the First MOT Due on a New Car?
For a new car, the first MOT test is typically due three years after its initial registration date. This initial test is crucial for ensuring the vehicle, even though new, meets all current road safety standards. If your tyres develop significant cracks before this first test, they could still cause a failure, highlighting the importance of regular checks regardless of vehicle age.
MOT Test Criteria for Tyre Condition
The MOT test has specific criteria for tyre condition, focusing on safety and roadworthiness. Understanding these rules helps you know exactly what an inspector is looking for and what constitutes a failure versus an advisory notice.
The MOT Testing Manual's Stance
The official MOT Testing Manual, which all authorised examiners must follow, outlines tyre requirements in detail. For tyres, the key areas of assessment include:
- Tread Depth: The minimum legal tread depth across 75% of the breadth of the tyre is 1.6mm. Less than this is a failure.
- Damage: This includes cuts, bulges, tears, and, crucially, cracks. The manual states a tyre will fail if there is 'evidence of delamination or cracking of the tread structure, ply or sidewall'.
- Inflation Pressure: Tyres must be correctly inflated for the vehicle's load.
- Tyre Type: All tyres on the same axle must be of the same type and construction.
- Size and Load Rating: Tyres must be of the correct size and have an appropriate load-bearing capacity for the vehicle.
The wording 'evidence of delamination or cracking' is key. It implies that the damage must be significant enough to be observable and to pose a risk. Shallow, superficial cracks that do not penetrate the rubber structure are unlikely to cause a failure on their own but may be noted as an advisory.
Understanding Advisory Notices
An advisory notice is not a failure. It means that while the vehicle has passed its MOT, there are aspects that may require attention in the near future. For tyre cracking, an advisory might be issued for minor, superficial cracks that do not currently compromise safety but could worsen over time. This is a helpful warning, allowing you to monitor the tyres and plan for replacement before they become a serious issue or fail a future MOT.
An advisory notice on tyre cracking serves as a crucial alert for ongoing maintenance.
When a Crack Becomes a Failure
A crack typically leads to an MOT failure when it is deep enough to penetrate the tyre's structure, affects its integrity, or is likely to lead to a rapid deterioration. This is especially true for sidewall cracks. Sidewalls are crucial for the tyre's ability to flex and absorb impacts. Deep cracks here can weaken the tyre significantly, making it prone to sudden failure. If the cracks are extensive, numerous, or appear to be 'checking' (small, interconnected cracks spreading across the surface), an examiner will likely deem them a safety hazard.
The Role of the MOT Testing Manual
The MOT Testing Manual is the definitive document for testers. It provides clear examples and criteria, ensuring consistency. For instance, under 'Tyres', section 7.1.3 discusses cuts and ruptures. It specifies that a tyre will fail if there is 'evidence of fabric or cords exposed or damaged' or 'bulging or separation'. Cracking that reaches this level of severity is a clear failure.
Solutions: Repairing or Replacing Cracked Tyres
When your tyre inspection reveals cracking, the question becomes: can it be fixed, or does it need replacing? The answer largely depends on the severity and location of the damage, and crucially, your safety.
When Replacement is the Only Safe Option
For MOT purposes and overall safety, deep cracks, sidewall damage, or any sign of delamination or exposed cords mean the tyre must be replaced. Attempting to repair such damage is generally unsafe and is not permitted for MOT compliance. The reason is that the structural integrity of the tyre has been compromised. The internal steel belts and rubber layers work together; if they are cracked or separated, the tyre can no longer withstand the stresses of driving, braking, and cornering, increasing the risk of a blowout.
Tyre replacement is non-negotiable for deep sidewall cracks.
If your tyres have significant cracking, the most sensible and safe solution is to replace them. This is especially true if the cracks are on the sidewalls, as this is the most vulnerable part of the tyre's structure. It's also a good idea to check the condition of all tyres on the vehicle, as tyres often degrade at a similar rate. If one tyre is cracked, others may not be far behind.
Can Minor Cracks Be Repaired?
In some very limited circumstances, minor surface cracking on the tread area *might* be repairable by a professional tyre specialist. However, this is rare for cracks that would be noticeable enough to be a concern for an MOT. Professional tyre repair involves plugging or patching from the inside. This is typically only suitable for punctures that have not damaged the tyre's structure. Most garages and MOT centres will err on the side of caution. If there is any doubt about the integrity of the tyre due to cracking, replacement will be recommended.
It's important to understand that tyre repair is a specialised job. A DIY repair is strongly discouraged and will not pass an MOT. Always seek advice from a reputable tyre shop. They will assess the damage and advise whether a safe repair is possible or if replacement is necessary. If the cracking is extensive or deep, they will confirm that replacement is the only viable solution.
Choosing Replacement Tyres
When you need to replace cracked tyres, consider factors beyond just size and price. Look for tyres that are appropriate for your vehicle's make and model, and consider your driving style. Reputable brands often use more advanced rubber compounds that resist cracking and degradation better than cheaper alternatives. Checking reviews and consulting with tyre professionals can help you select tyres that offer good longevity and safety performance.
Preventing Future Tyre Cracking
Preventing tyre cracking is a proactive approach to vehicle maintenance that not only helps ensure you pass your MOT but also contributes to overall road safety and tyre longevity. By adopting a few simple habits, you can significantly reduce the risk of your tyres developing problematic cracks.
Proper Inflation is Key
Maintaining the correct tyre pressure is perhaps the single most effective way to prevent premature wear and stress that leads to cracking. Under-inflated tyres flex excessively, generating heat and stressing the sidewalls, while over-inflated tyres can become brittle and more susceptible to impact damage. Check your vehicle's handbook or the sticker on the driver's door frame for the recommended pressures and check them at least once a month when the tyres are cold. An accurate tyre pressure gauge is a worthwhile investment.
Regular Cleaning and Protection
Tyres are made of rubber, and like most rubber products, they degrade over time due to exposure to UV rays and ozone. Parking your car in a garage or shaded area whenever possible can shield the tyres from direct sunlight. When washing your vehicle, use a mild soap and water to clean the tyres, and consider using a water-based tyre dressing. Avoid products containing harsh chemicals or petroleum distillates, as these can accelerate rubber degradation and lead to cracking. Some dedicated tyre protectants can offer an additional layer of defence against UV damage.
Store spare tyres properly: if you have a spare tyre stored for a long time, ensure it's kept in a cool, dark place away from direct sunlight, chemicals, and heat sources to prevent premature ageing.
Mindful Driving Habits
Aggressive driving – such as rapid acceleration, harsh braking, and sharp cornering – puts unnecessary stress on your tyres. While this is more directly linked to tread wear, it can also contribute to structural fatigue over time. More importantly, avoid kerbing your wheels or hitting potholes at speed. These impacts can cause internal damage that may not be immediately visible but can weaken the tyre structure, leading to cracks developing later. A careful driving style not only saves your tyres but also improves fuel efficiency and overall vehicle safety.
Rotation and Alignment Checks
Regularly rotating your tyres can help ensure they wear more evenly, preventing excessive stress on specific areas that might otherwise lead to premature cracking. Along with rotation, having your wheel alignment checked periodically is also beneficial. Misaligned wheels can cause uneven tyre wear and put undue stress on the tyre structure, potentially contributing to cracking over the long term. It is advisable to have your wheel alignment checked if you notice uneven tyre wear or if your vehicle pulls to one side.
Age of Tyres
Finally, remember that tyres have a finite lifespan, irrespective of tread depth. The rubber compounds degrade over time. Most experts recommend replacing tyres that are more than six years old, and certainly no longer than ten years, even if they appear to be in good condition. The manufacturing date is stamped on the sidewall. If your tyres are approaching or exceeding this age bracket, consider replacing them proactively, even if you don't see obvious cracking, as the internal structure may be compromised.
Bodywork and Tyres: A Holistic MOT View
While this article focuses on cracked tyres and their impact on your MOT, it's important to remember that the test is a comprehensive inspection of your entire vehicle. A holistic view of your car's condition is crucial for a successful MOT.
Beyond the Tyres: Other Critical Areas
The MOT test covers a wide range of components, including:
- Brakes: Essential for stopping power and safety.
- Lights: All lights must be functioning correctly and be the correct colour.
- Steering and Suspension: Components like shock absorbers, ball joints, and steering linkages are checked for wear and tear.
- Exhaust System: Checked for leaks, corrosion, and noise levels.
- Chassis: Structural integrity, looking for excessive corrosion or damage.
- Windscreens: Chips or cracks in certain areas can cause failure. A windscreen MOT failure is common.
Just as cracking in a tyre compromises its function, significant corrosion or damage to the vehicle's bodywork can also lead to an MOT failure, particularly if it affects structural integrity or sharp edges are exposed.
The Interplay of Tyre Wear and Vehicle Dynamics
Tyre condition affects more than just the MOT. Worn or damaged tyres can impact your vehicle's handling, braking distances, and fuel efficiency. For example, if your tyres are significantly under-inflated or damaged, it can put extra strain on your suspension and braking system, components that are also rigorously checked during an MOT. A dodgy MOT test often comes down to multiple minor issues combining into a failure, or one critical component being severely compromised.
Ensuring your tyres are in good condition is fundamental to your vehicle's overall safety performance.
Preparing for the MOT Test
Before taking your car for its MOT, it's wise to perform a thorough pre-MOT check yourself. This includes:
- Checking tyre tread depth and condition (including any cracks).
- Ensuring all lights are working.
- Checking the windscreen for damage in the driver's line of sight.
- Verifying that your horn works.
- Checking fluid levels (though not a failure point, low levels can indicate other issues).
By addressing potential issues like cracked tyres proactively, you significantly increase the chances of a smooth MOT pass and, more importantly, ensure your vehicle is safe to drive.
Special Considerations: MOT Exemption and SORN
Some older vehicles may be MOT exempt, but this does not absolve owners of the responsibility to maintain their vehicle in a roadworthy condition. For those who declare their vehicle 'off the road' using a Statutory Off-Road Notification (SORN), driving it to an MOT test is one of the few exceptions to the rule that a SORN vehicle cannot be used on public roads. However, you cannot drive a SORN car to an MOT without insurance, as it still needs to be insured for the journey to and from the test centre.