Tyre Tread Depth – A Complete Guide

Your tyres are what connect you and your car to the road surface. Consequently checking your tyres are in good condition and there is adequate tyre tread is very important to stay safe on the road. Doing a quick visual check periodically is easy to do and could be a life saver. We explain how you can identify worn tyres and what to do next.

What is tyre tread?

The tread of your tyre is designed to increase the grip your tyres can hold over the road surface. Especially in wet weather conditions when it helps to disperse water away from the contact patch between the tyre and road. When your tyre wears down, its ability to retain its grip on the road decreases, which means longer stopping distances and a greater risk of aquaplaning.

What is the minimum legal tyre tread depth?

In the UK and EU the minimum tyre tread depth is 1.6mm for passenger cars, this should be present all-round the central three-quarters of the tyre.

Driving with a tyre with below minimum tyre tread in the UK can land you a fine of £2,500 and three penalty points, per tyre. So if all 4 tyres on your vehicle are worn too much you may be fined £10,000 and potentially you may lose your licence in the process.

Aside from the legal limit, various tyre manufacturers and experts recommend having at least 3mm tread. Having adequate tyre tread can boost a tyre’s ability to retain grip on the road surface and significantly decrease braking distances. Particularly in wet weather worn tyres are particularly hazardous.

According to research commissioned by the British Rubber Manufacturers Association on varying tread depths, the stopping distances start to increase dramatically at tread depths of below 3mm. At the legal minimum tread depth of 1.6mm, the stopping distance is increased by 36.8% on hot-rolled asphalt and 44.6% on smooth concrete.

How to check whether your tyre tread is within the legal limit

To check the tyre tread depth you will normally need either a tyre tread gauge or simply a 20 pence coin. Some tyres come with a built-in wear indicator which would require no tool to check.

Checking tyres with a 20p coin

20p coin tyre tread test

A 20p coin is used for this test as the outer edge is about 2mm. To gauge the tread depth take a 20p coin and insert it into the tread grooves across the central three-quarters of the tyre.

Your tyres will be above the legal limit if you can’t see the band on the coin.

However, if you can see the band on the coin, your tyres could be below the legal limit and are likely very unsafe. You should then get them inspected by a mechanic.

20p tyre tread test - legal tread

20p tyre tread test – coin band not visible so tyre above legal tread depth limit

This method is not nearly as precise as using a gauge but will show you that you are within the legal limit of having 1.6mm tread left. We recommend drivers conduct the 20p test at least once a month and especially before long journeys.

Checking tyres with tyre tread depth gauge

A more precise option to check your tyre tread is by using a tyre tread gauge. For the gauge all you have to do is insert the point into a part of the tread and it will then show you in mm how much tread is left on the tyre.

Tyre tread depth gauges retail for about £5 and there are also devices that serve the dual purpose of checking tyre tread depth as well as tyre pressure.

When should you check your tyres and tread depth?

Tyres should be checked periodically, and certainly before long or important journeys. It’s suggested to check the tyre tread at least once a month.

It’s important to remember that tyres are very important in keeping your car connected to the road and in enabling you to brake safely. It could be argued that tyres should even be subjected to a quick check a few times a month, if only because it’s very easy to do and you can be aware of any wear and tear you wouldn’t otherwise notice until it’s too late.

Do I need to replace my tyres if it’s below the legal tread limit?

Yes, it is illegal to drive a vehicle with a tread depth of tyres below 1.6mm and you will need to replace your tyres. It is recommended that you check tyre tread depth at least once a month so you can replace the tyre before it reached the legal limit to ensure overall safety.

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Low profile tyres: tyre tread depth

Low profile tyres usually mean that the tyre is fitted to a larger diameter wheel. They have more contact with the road and stability due to larger tread widths, which make these very popular, however, more contact with the road will make low profile tyres wear out faster.

To ensure the safety of these tyres and optimum grip, it is recommended that you check tyre tread depth regularly, especially for low profile tyres.

What is a bald tyre and how to spot one?

A bald tyre is generally a tyre that’s very clearly worn out across its contact surface and no longer has any or almost no tread on it, having worn below the minimum 1.6mm tread depth. This state of degradation is particularly dangerous as these tyres cannot, in wet conditions, disperse water adequately and retain contact with the road. A car will aquaplane in a situation like this, leading to dangerous situations on the road. If you think you have a bald tyre on your vehicle it’s very important to get it replaced as soon as possible.

Illegal tyres examples

Tyres with a tread depth below the legal limit might be the most common example of illegal tyres, there is however a host of other horror examples of illegal types of tyres.

Over-inflated tyres

Overinflation of a tyre can lead to illegal wear in the centre of the tyre as the tyre bulge under pressure. The tyre tread will wear away much more rapidly in that area. Always ensure you check the tyre pressures recommended by your car manufacturer.

Under-inflated tyres

The opposite to over-inflated tyres, with under-inflated tyres the middle section will collapse meaning that most of the weight is carried by the outer edges of the tyres, leading to uneven wear on the edges.

Cuts

In some cases, sharp objects from the road can create nasty cuts in tyres, and sometimes tyres may be subject to malicious damage by tyre slashers. These may not fully puncture the tyres but are dangerous to drive with.

Uneven wear

Often uneven wear across a tyre’s contact patch is caused by wheel alignment or potentially other suspension issues. For example through excessive camber wear.