UK TYRE LAW & TREAD DEPTH

Your tyres are the only part of your vehicle that's in contact with the road. So the condition of your tyres is key to your safety.

It’s the law to make sure your tyres have a minimum tyre tread depth. Find out what the law says and learn how to check your tyres here.

What is the legal tyre tread depth?

The legal minimum tyre tread depth varies by each type of vehicle.

Testing your tread depth

There are a few different ways you can check your tyre tread to make sure you don’t have worn tyres and that they meet the legal minimum tread depth.

Tread wear indicators

The easiest way to check your tyre tread's legal is to look out for tread wear indicators. These are usually small bars, about 5mm wide, built into the base of the tyre's main grooves.

• If the tyre tread is level with the top of the wear indicator, it means your tyres have reached the legal limit of 1.6mm.
• When tyres are worn to this level, they need to be replaced.

Tyre gauges

The best method for testing your tyres is to use a calibrated tyre gauge. These come in many different forms – from digital gauges to laminated cards with coloured indicators.

• To use, place the gauge into the tyre’s groove.
• The gauge will show you how close you are to reaching the required minimum depth for your vehicle.
• Check the tyre tread regularly and at different places across the tyre so you can watch out for worn tyres and spot any early signs of uneven wear.

The 20p test

If your tyres don't have tread wear indicators and you don’t have a gauge, then you can test them with the 20p tyre test. The outer rim of a 20p coin is just under 3mm wide.

• Place a 20p coin into your tyre’s tread grooves.
• If the outer rim of the coin is obscured then your tyre's comfortably above the legal minimum tread depth.
• If you can see part of the rim of the coin then it's time to check your tyres more carefully using a proper tyre tread depth gauge.

When should you change your tyres?

Check your tyre tread depth more often once they get down to 3mm. Aim to replace tyres before the tread wears below 2mm.

Changing your tyres is more important as autumn and winter approach. It’s better to get new tyres before winter than struggle through the cold and wet with tyres approaching the legal minimum tread depth.

You should get around 20,000 miles out of your front tyres before they wear down, and about 40,000 from your back tyres.

Read more about tyres:

• How to safely change a flat tyre
• Find out how long tyres last

What causes tyre wear?

Tyres will start to wear out over time, but some factors can increase the wear.

• Driving style – Aggressive cornering and braking increases wear.
• Position – The tyres on the driven wheels will wear more quickly and even more so on front wheel drive cars as these handle the steering too.
• Speed – High speed driving increases temperature and wear.
• Load – Excess load increases wear, as does vehicle weight. Tyres on heavier cars will wear faster.
• Pressure – Under inflation (through increased flexing and temperature) and over inflation (through reduced contact area) can both increase wear.
• Alignment – Tyres will wear quickly and unevenly if wheel alignment is wrong of if suspension components like shock absorbers are worn.

Dangers of driving with a low tyre tread

Driving on tyres with tread below the legal limit can be incredibly dangerous, as well as illegal. It’s even worse driving with bald tyres where the tread has worn away altogether.

Hazards of driving with worn tyres include:

• Less grip on wet roads.
• Longer stopping distances.
• A greater risk of aquaplaning.
• Less traction on icy roads or snow.
• More chance of punctures, which can lead to a sudden blowout.

If you change your tyres when the tread wears down, you’ll have better grip on the roads and less stopping distance.

What if I get into an accident with illegal or dangerous tyres?

If you’re involved in an accident and your tyres don’t meet the legal minimum standards, any insurance claim you make could be invalidated.

If you drive with tyres that are dangerous because they’re worn or bald, you could be prosecuted for using a vehicle in a dangerous condition.

If could get you a fine of up to £2,500 and 3 points on your licence. And that’s just per tyre. If all 4 tyres are found to be dangerous, you could be looking at a £10,000 fine and 12 points.

Other legal tyre requirements

Because they play such a vital role, there are 2 specific requirements for legal tyres.

1. Tyres must be fit for purpose and be free from any defects which might damage the road or endanger any person.

To be ‘fit for purpose’, tyres must not have:

• Any lumps, bumps or bulges, as these can mean structural damage.
• A cut or tear bigger than 25mm or 10% of the width of the tyre, whichever is greater, and which is deep enough to reach the ply or cord.
• Any part of the ply or cord exposed.

2. Tyres must be inflated to the right pressure.

That means sticking to the pressure recommended by both your vehicle manufacture and the tyre manufacturer.

What should my tyre pressure be?

Tyre pressure isn’t ‘one size fits all.’ Each car will have its own recommended pressures. You can find these inside the driver’s door, inside your petrol cap or in the owner’s manual.

You'll fail an MOT if your tyres have any of these faults or if you have tyres of different sizes on the same axle, so make sure you check your tyres before you book an MOT.

Find out more about tyre pressures.