Tyre tread depths explained

Ask yourself this: exactly how often do you check the tread depths on your car’s tyres? It’s easy to become complacent and only check the amount of tread left on your tyres before an MOT test. However, it’s such an important task that it should be done way more often, especially given how easy it is.

Why is it so important? Well, regardless of the type of car you drive, the tread depth of your tyres plays a crucial role in how much grip your car has on the road. Having sufficient grip from your tyres is of paramount importance for your safety, not to mention the safety of your passengers and other road users. Most modern cars have advanced electronic safety systems such as anti-lock brakes (ABS) and electronic stability control (ESP) to help maintain grip when you're driving. However, these systems require a set of good, roadworthy tyres to perform optimally.

Why is tyre tread important?

No matter how large your wheels and tyres are, only a tiny amount of each tyre makes direct contact with the road surface at any one time. The ‘contact patch’, as it’s known, is essentially the same size as the palm of your hand, so you want to maximise the amount of grip it has.

Car tyres have grooves running around their circumference, and the depth of these grooves is referred to as their ‘tread depth’. The greater the tread depth, the less worn your tyres are, and the better they can be expected to grip onto the road, as they channel water away from the contact patch.

With such a tiny amount of material expected to do so much work, it’s important that each tyre can perform at its best. This means it’s vital to make sure that your tyres are in good condition, by checking that their tread depth is sufficient.

Follow our guide for all you need to know about tyre tread depths.

UK legal minimum tyre tread depth

UK law states that car tyres must have a minimum tread depth of 1.6mm across 75% of the surface area. In other words, if you imagine a line at the centre of the tread in the direction of the car’s travel, the tyre must have at least 1.6mm of tread measured across three quarters of the tyre’s surface from this centre line. This tread must be consistent around the whole tyre. Drivers that are found to be on the road with tyres below the minimum tread depth can receive a fine of up to £2,500 and a maximum of 3 penalty points on their licence.

However, while this is the legal minimum requirement, we strongly advise replacing your tyres when the tread depth reaches 3mm. That’s because the amount of grip provided below this threshold reduces drastically.

When a tyre is brand new it will usually have a tread depth of around 8mm. However, winter tyres often carry significantly more.

What does tyre tread do?

Tyre tread is designed to disperse water from underneath the tyre. As a wheel rotates, the grooves in the tyre tread act like a pump, sucking water away from the contact patch - effectively drying the road surface so that the rubber on the tyre can grip onto it more effectively. A tyre in good condition can move around 15 litres of water every second.

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A reduced level of tread reduces the tyre’s ability to do this. Because the tyre can only grip the road, and not displace the water on its surface, you run the risk of aquaplaning in wet conditions – that means literally skimming on the water trapped between the tyre and the road surface. If this happens, you could be unable to steer or brake. Tyres kept in good condition with plenty of tread depth, can prevent this dangerous situation.

Tyre tread wear indicators

It's recommended that you check your tyres at least once every two weeks. A visual check only takes a few minutes and could save you from having a nasty accident. Most tyres have tread depth wear indicators moulded into the rubber. These take the form of rectangular horizontal ridges in the tread. As the tyres wear, they get closer to the tyre’s surface. When they become flush with the surface of the tyre, it means the tyre needs immediate replacement.

How to check tyre tread depth

Although the wear indicators provide a quick visual indication that your tyres are reaching the legal minimum tread depth, it’s still a good idea to have a closer look as regularly as possible. According to the UK road safety charity, TyreSafe, a staggering 1 in 5 people don’t perform this crucial check. An effective and easy way to do this doesn’t take any specialist tools and can be performed with a 20p coin.

Take the coin between your finger and thumb and insert the edge in the gaps at multiple points across the tread. A 20mm coin has a rim approximately 3mm deep, so if the tread height doesn’t come up past this mark, it’s an indication that the tyre is very close to requiring replacement.

For a more precise indication of your tyre tread depth, a tread depth gauge can be obtained inexpensively from any good car-accessory store.

The depth of your tyre tread is very important for safety. If you don’t feel confident about checking your tyres, or would rather not make a judgement for yourself, most tyre shops will happily check the tread depth of your tyres. They’ll also offer an assessment of the condition of your tyres in general.

It’s worth having a good relationship with a local tyre supplier. If you’re familiar with the staff and are likely to choose them to supply your tyres when the time comes, they’ll be only too pleased to check your tyres on request, free of charge.

Do you need help choosing your next set of car tyres? Read our guide on tyre speed rating and labelling, or on choosing the best car tyres and the best all season tyres to buy.