Tyre pressures and tread depths: your safety check guide

Stay safe and save money by checking your car tyre pressures and tread wear regularly

It’s all too easy to take tyres for granted, but when you remember they’re the only physical point of contact between your car and the road – and that not keeping them in good order could land you with a hefty fine – you should sit up and take note. It’s key to remember the vital importance of checking your car’s tyre pressures, tread depth and general condition on a regular basis.

The legal tyre tread limit is 1.6mm, although drivers are generally advised to change them once they get down to 3mm. If the police catch you driving with tyres worn below the legal limit, you could be fined £2,500 and given three penalty points – and that’s per tyre. If caught with a full set of illegal tyres, you’ll face a £10,000-fine and potentially lose your licence.

Best tyre pressure gauges

Another reason why checking your tyres is a sensible thing to do is that neglected tyres cost money. If tyre pressures aren’t kept to the correct levels, it not only increases fuel consumption, but also increases wear on various components. The reason being, a flat or underinflated tyre has more resistance to rotating due to the higher surface area of rubber being in contact with the road. This explains why cars with flat tyres pull to one side.

Also, bashing your tyres on the kerb regularly puts stress on the side walls and can increase the likelihood of malfunction. The condition of your tyres is possibly the most important aspect of vehicle safety, while fuel economy and your car's handling will also be affected by damaged or worn tyres. A puncture is one issue to deal with, but tyres can lose air pressure over time, so you should regularly check that all four tyres on your car are inflated to the correct pressure.

The correct tyre pressures for your car will be in your car's handbook (possibly spelt 'tires' if you happen to have a handbook from across the pond), and it will probably say to check them on a weekly basis. This isn't strictly necessary, although no expert would advise leaving tyres unchecked for more than a month.

As tyres are the only point of contact between your car and the road, tyre condition is arguably one of the most important aspects of vehicle safety.  A puncture can have immediate and devastating effects, but tyres can also suffer from an aptly named ‘slow puncture’, on top of naturally decreasing in pressure over time. It is because of the last two, that it is very important to regularly check your tyre pressures.

Legislation has made it easier to check tyre pressures, because since 2014, all new cars sold in the EU must come with a tyre-pressure monitoring system (TPMS). This systems use sensors within the car's wheels that can detect a drop in air pressure. This will then flash up a warning on the car's dashboard if it falls below a certain level, usually telling you which corner is affected. If you’ve bought a new car in the last year or two, then it’s likely to come fitted with TPMS.

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If your car doesn’t have TPMS, you can retrofit it with aftermarket kits, and anyway it's easy to check your pressures using a manual or digital tyre pressure gauge. You can use the equipment provided on garage forecourts, although there’s often a small charge, and the system may not be the most accurate. Either way, the procedure for checking your pressures is the same.

How to check your car tyre pressures

Tyre pressure is measured using two units: bar (where 1 bar is the pressure of the Earth’s atmosphere at sea level) and pounds per square inch (shortened to psi). Most gauges will display both units, and so will your car’s handbook, which lists the recommended pressures. Most cars also have a sticker or plate on the inside of one of the doorframes or on the fuel filler flap with a table of pressures.

To check your pressures, you need to find each wheel’s tyre air valve, which is a small tube that sticks out of the wheel rim. Each one should have a little plastic screw-on cap dust cover, which you can easily unscrew by hand. Make sure you place it somewhere safe and don’t forget to screw it back on tightly when you’re finished.

Once the dust cap is off, you can place your pressure gauge over the valve, push it in slightly and hold it for a few seconds. A pressure reading should appear on the gauge’s dial or screen.

If any of your tyres aren’t at the correct pressure, the machines on garage forecourts can be programmed to pump them up – you simply input the correct pressure and it does the rest. If you’re at home, you can use a powered or foot-operated air pump to add air to the tyre, then check the pressure again to verify you’ve put enough in.

How to check tyre tread depth and condition 

While you’re checking your tyre pressures, you should give them a visual inspection as well. Look for any nails or other sharp objects that may have become stuck in the tread, and watch out for any odd-shaped bulges in the tread surface or sidewall of the tyre.

If you do spot anything, head to a tyre centre or garage straight away, as damaged tyres like this can blow out without warning, potentially causing you to lose control of your car.

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You should also pay close attention to your tyre tread depth. The law requires a minimum tread depth of 1.6mm in a continuous band around the central three quarters of the tyre. You can check the tyre’s tread depth with a tyre tread depth gauge, but for a quick visual check, manufacturers often mould little bars into the tread at a height of 1.6mm.

When the main tread blocks wear down to the height of the little bars, it’s time for a new tyre. Of course, we would always recommend changing your tyres well before they reach the legal minimum tread depth.

Check out our in-depth test on the best all season tyres…

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