What is the legal tyre depth and when should I replace my tyres?

Last updated October 28, 2021

10% of cars fail their MOT due to tyre issues, but even if you aren’t handy with a spanner, checking your tyres’ condition is non-negotiable. Fortunately, it’s quick and easy to conduct the basic tyre checks, this typically involves checking the tread depth, tyre pressure and any signs of wear.

The following guide provides all the information you need on the legal tyre tread depth, tyre pressure, when you should replace your tyres and more.

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Why do tyres have a tread pattern?

New tyres feature symmetrical tread patterns to deliver smooth driving, high directional stability and low rolling resistance. What’s more, even tyre tread on or above the legal limit provides robust protection against aquaplaning, excellent handling in snow and assured road holding at high speeds.

What is the legal tyre tread depth?

The primary aspect of tyre safety is tread depth. Tyre tread depth refers to the deepness of the grooves covering the tyre’s circumference.

The tread depth on tyres is usually around 7mm, but the legal tread depth is 1.6mm.

How to check tyre tread depth

Most tyres have tread wear indicators, which are hard, raised bars at the bottom of each groove – tyres have reached their legal limit when the tread is level with these bars. However, it’s best not to rely on this indicator alone, as uneven tyre wear is a common problem.

Incorrect wheel alignment or a worn suspension can produce uneven wear to the inside or outer edge of the tyre while leaving the tread bar intact. You can check your tyres’ condition by running a 20p coin along the tread – the outer edge of a 20p is 1.6mm thick, so if the tread is below this mark it’s most likely below the legal tread depth.

Should you run a tyre to the legal limit?

While the legal limit for tread depth is 1.6mm, many tyre manufacturers, suppliers and motoring groups recommend replacing your tyres at 3mm.

Whether you replace them at 1.6mm, 2mm, or 3mm is down to personal preference and the tyres’ quality. However, it’s worth noting that tyres near or on the legal limit may be more susceptible to aquaplaning as there’s less tread depth to disperse water.

Tyre tread example

A tyre with 2mm of tread may not perform as well as one with 3mm on a road with 2.5mm water on its surface. With this in mind, it’s probably best to be cautious and replace them around 3mm.

Tyre damage

Aside from becoming worn, tyres are susceptible to internal damage. However, unlike a puncture or excessive wear, internal damage can be difficult to identify, particularly when there is no immediate impact on the car’s handling. Watch out for potholes too, as driving over them can lead to severe ramifications.

Signs of tyre damage

Bulges, blisters or splits in the sidewall are typically indicators of severe internal tyre damage. Sunlight can cause cracks as well, although this tends to occur on cars left outside in hot weather for extended periods. Therefore, it’s best to check your tyres weekly as damage can result in a loss of pressure, or worse, a sudden blowout.

Run flat tyres

Run flat tyres are self-supporting and work even after sustaining a puncture and due to their reinforced sidewalls, run flats are less susceptible to blowouts.

However, they’re not indestructible and you’ll need to inspect their tread and condition regularly. Bear in mind that, unlike standard tyres, run flats cannot be repaired so you'll have to replace them immediately once they're damaged.

When should I replace my tyres?

A tyre's lifespan ultimately depends on your vehicle, driving style and climate, among other factors. Many manufacturers recommend getting your tyres checked after five years of use. However, if you don't record many miles, ten years is the recommended timeframe for changing your tyres, even if they appear to be in usable condition. The same rules also apply to spare tyres.

What should my tyre pressure be?

Maintaining the correct tyre pressure is vital, as underinflated or overinflated tyres can rapidly increase wear and affect your car's handling.

You'll find the correct pressures for your car's tyres inside the fuel filler flap or in your owner's manual. Where possible, use the same pressure gauge to keep all readings consistent and check them weekly.