How to check your tyre tread depth

Your tyres are the only part of the car that touches the road, and tread depth is checked at every MOT. Checking it yourself only takes a few minutes and needs nothing more than a coin or a tread depth gauge. Here's how to do it, and what the wear pattern can tell you about the rest of the car.

The legal limit: 1.6mm

In the UK, a car's tyres must have at least 1.6mm of tread across the central three-quarters of the tread, around the whole circumference of the tyre. That applies to every tyre on the car, and it's one of the things the MOT tester measures. The tester also looks at the condition of each tyre and checks that the tyres on the same axle are the same size and type.

1.6mm is the legal minimum, not a target. Wet grip falls as the tread wears down towards the limit, and TyreSafe, the UK tyre safety organisation, says the minimum commonly advised by tyre and safety experts is 3mm.

The 20p test: a quick rough check

A 20p coin gives you a quick idea of whether your tread is getting low:

1. Pick any stones or dirt out of the tread.
2. Put a 20p coin into one of the main grooves, the deep ones that run all the way round the tyre.
3. Look at the raised outer band around the edge of the coin.
4. Repeat in several places around each tyre and across its width.

If you can see the outer band of the coin, the tread may be getting low and should be measured properly with a gauge. If the band is hidden, that's a good sign, but the coin is only a rough guide, not the legal test. A gauge is the better way to be sure.

Using a tread depth gauge

A tread depth gauge gives you an actual reading in millimetres. Push the probe into a main groove until the base sits flat on the tread blocks either side, then read the figure. Measure the inner, middle and outer main grooves, at several points around the tyre, because tread doesn't always wear evenly. The lowest reading is the one that counts.

Most tyres also have tread wear indicators: small raised bars moulded into the bottom of the main grooves. When the tread has worn down level with these bars, the tyre is at or very close to the legal limit and needs replacing.

What uneven wear tells you

While you're measuring, compare the depth across the width of the tyre. Uneven wear is often a sign of something else that needs sorting:

• Both outer edges worn more than the centre: often a sign the tyre has been running under-inflated.
• The centre worn more than the edges: often a sign of over-inflation.
• One edge worn much more than the other: can point to a wheel alignment problem, for example after hitting a kerb or a pothole.
• Patchy or irregular wear: can point to worn suspension parts.

A new tyre will wear the same way if the cause isn't put right, so if you spot uneven wear, have the pressures, alignment and suspension checked before or when you replace the tyre.

Other tyre checks while you're there

• Cuts, lumps and bulges in the tread or sidewall. A lump or bulge can mean damage inside the tyre and should be looked at by a tyre specialist. At the MOT, a cut deep enough to reach the cords or a bulge from structural damage will fail.
• Objects in the tread, such as stones, glass or nails.
• Pressures. Tyres must be inflated to the car maker's figures for the load you're carrying. You'll find them in the handbook, and often on a label inside the fuel filler flap or the driver's door opening. Check them with the tyres cold.
• Matching tyres. Tyres on the same axle must be the same size and type.
• The tyre pressure warning light. On cars first used on or after 1 January 2012, the tyre pressure monitoring warning light is checked at the MOT.

The spare wheel isn't inspected at the MOT, but it's worth checking its condition and pressure anyway so it's ready if you need it.

How often to check

TyreSafe suggests checking your tyres at least once a month and before long journeys. Checking the tread and the pressures at the same time makes it an easy habit, and it means there are no surprises when the MOT comes round.

Find tread depth gauges, pressure gauges and tyre inflators in our tyre tools range, and add your car to My Garage to check its MOT history and sign up for an MOT reminder email.