When it comes to car maintenance, there’s one safety-critical check you may overlook easily: tyre tread depth. Your tyres are the only part of your vehicle that makes contact with the road, and if they’re not in good condition, your safety is immediately in danger.
A 2020 survey revealed that 69% of UK drivers didn’t know the legal minimum tread depth. If you’re part of that statistic, don’t worry. We are here to help. If you’re wondering how to check your tyre tread depth, we’ll walk you through everything you need to know, as well as why it matters, how to check it using the 20p coin test, and what the law says about it in the UK.
What is Tyre Tread Depth and why is it important?
Tyre tread refers to the grooves in your tyre. These patterns are specially designed to channel water away from the tyre surface, helping your car maintain grip on the road, especially in wet or icy conditions. As tyres wear over time, these grooves become shallower, reducing their effectiveness.
Here’s why tyre tread depth is crucial:
- Shorter Stopping Distances The deeper the tread, the better your grip. This means a shorter stopping distance, especially in emergencies. Shallow treads significantly increase your braking distance, making collisions more likely.
- Better Aquaplaning Resistance Aquaplaning happens when water builds up under the tyre, causing the car to skid uncontrollably. Proper tread depth disperses water efficiently, sometimes as much as a bucket of water every 7 seconds. Worn tyres can’t do this effectively, which can put you in serious danger.
- Avoiding Legal Penalties Driving on illegal tyres isn’t just dangerous, but also expensive. If you’re caught with tyres below the legal tread limit, you could be fined £2,500 per tyre and receive 3 penalty points per tyre. That’s a potential £10,000 fine and 12 points if all four tyres are worn!
What Is the Legal Minimum Tyre Tread Depth in the UK?
UK law requires your tyres to have at least 1.6mm of tread depth across the central three-quarters of the tyre, around the entire circumference. However, many experts and manufacturers recommend replacing tyres at 3mm. Below that level, stopping distances can increase by up to 44% in wet conditions.
How to Check Your Tyre Tread Depth; Introducing the 20p Tyre Tread Test
If you don’t own a tread depth gauge, the 20p coin test is a brilliant DIY alternative. It’s free, takes seconds, and can help you stay safe and legal on the road.
How to Do the 20p Test:
- Take a standard 20p coin.
- Insert it into the main grooves of your tyre tread.
- Check if the outer band of the coin is visible.
- If the outer band is obscured, your tread is above the legal limit.
- If you can see the outer band, your tread is likely below 1.6mm and you should replace your tyre immediately.
Pro Tips:
- Test at least three different places around each tyre, because tread wear can be uneven.
- Repeat this test once a month and before any long journey.
How to Check Your Tyre Tread Depth: Other Ways
While the 20p test is incredibly handy, here are two more accurate ways to check your tyres:
1. Tread Wear Indicators (TWIs)
Many tyres include built-in markers inside the grooves. Once the tread wears down to the level of these indicators, your tyres need replacing.
2. Tyre Tread Depth Gauges
These tools are available in both digital and analogue forms. Insert the gauge into the tread and it will display the exact depth in millimetres.
3. Tyres and the MOT Test
Tyre tread depth is a key part of your annual MOT. Bald or under-treaded tyres are one of the most common causes of MOT failures.
If your tyres are below 1.6mm, your vehicle will fail its MOT. Checking them before your test can:
- Save you from a retest fee.
- Give you time to find tyres in your budget.
- Keep your vehicle road-legal.
What Happens If You Drive on Illegal or Bald Tyres?
Here’s what you risk:
- Fines of up to £2,500 per tyre.
- 3 penalty points per tyre.
- Invalidated insurance claims if you’re in an accident.
- Increased risk of tyre blowouts, reduced grip, and loss of control.
- MOT failure
When Should You Replace Your Tyres?
Knowing when to replace your tyres is essential for both safety and compliance with UK road laws. As a general rule, many tyre and safety experts recommend replacing your tyres once the tread depth reaches 3mm. Although this is above the legal minimum, it’s widely accepted that performance begins to deteriorate significantly below this point.
If your tyres are at 2mm, you’re entering the danger zone, with an estimated 1,000 miles of safe driving left. This should act as a final warning to arrange a tyre replacement before the situation becomes critical. Once your tread reaches the legal minimum of 1.6mm, or worse, drops below it, your tyres are considered both unsafe and illegal. At this point, immediate replacement is not just recommended, it’s a legal requirement.
Beyond tread depth, there are other warning signs that your tyres may need changing. Keep an eye out for visible damage such as cracks, bulges, or deep cuts, as these could indicate structural weaknesses that could lead to sudden failure. Embedded debris, like nails or glass, can cause slow punctures or even blowouts. Uneven wear across the tyre surface could suggest issues with your vehicle’s alignment or suspension, and should be addressed by a professional to avoid premature tyre wear.
Stay Safe With the 20p Test
To keep your tyres in optimal condition, perform regular maintenance checks. The 20p test should be done monthly, and tyre pressure should be checked just as often, especially before long journeys. Visually inspect your tyres for any signs of damage or wear, and rotate them every 6,000 miles to promote even tread wear. It’s also wise to consider replacing your tyres ahead of winter, as colder, wetter conditions demand maximum grip for safe driving. Staying on top of tyre maintenance not only ensures your vehicle remains road legal but also gives you peace of mind behind the wheel.
