Winter tyre check: tread depth, pressures and using a tyre inflator

Your tyres are the only part of the car that touches the road, and in winter, when roads are wet, cold and often covered in leaves, grit or slush, they have a harder job than at any other time of year. A ten-minute check of tread depth and pressures before the weather turns is one of the most useful things you can do for your car. Here is what the law says, how to check both properly, and how to use a portable tyre inflator to put things right at home.

The legal minimum tread depth in the UK

The Highway Code's Annex 6 on vehicle maintenance sets out the rule for cars: tyres MUST have a tread depth of at least 1.6 mm across the central three-quarters of the breadth of the tread and around the entire circumference. Both parts matter. A tyre that has plenty of tread in the middle but is worn down in one patch, or around one edge of the central band, can still fall short.

The consequences of getting it wrong are not trivial. The RAC's guide to checking tyre tread points out that drivers can face a fine of up to £2,500 and three penalty points for each illegal tyre. Tyres are also checked at the MOT, and the MOT inspection manual's section on axles, wheels, tyres and suspension lists tread below the legal limit as a defect.

The legal limit is a minimum, not a target. Plenty of drivers choose to replace tyres before they reach it, especially ahead of winter, because deeper grooves help clear water from the contact patch.

How to check your tread depth

• Use a tread depth gauge. Push the probe into a main groove, slide the body flat against the tread blocks and read the measurement. Gauges are inexpensive and far more reliable than guessing by eye.
• Check several points on each tyre. Measure across the width – inner, middle and outer grooves – and at several places around the circumference. Roll the car forward a little to reach the section that was sitting on the ground.
• Look for tread wear indicators. Most tyres have small raised bars moulded into the bottom of the main grooves. When the surrounding tread wears down level with them, the tyre is at or very near the limit.
• Do not forget the inner edge. Wear on the inside shoulder is easy to miss because you cannot see it without crouching down or turning the steering. Uneven wear can be a sign that the wheel alignment needs checking.

While you are down there, look over each sidewall and the tread for cuts, bulges, cracks or embedded objects such as nails or glass. Anything that looks like a bulge or a deep cut should be checked by a tyre professional before you drive any distance.

Checking tyre pressures properly

Annex 6 also advises checking tyre pressures at least weekly, and doing it when the tyres are cold. That second part matters: after a drive the air inside warms up and the pressure reads higher, so a check at the petrol station at the end of a long journey can mislead you into letting air out. Ideally check first thing in the morning, or after the car has been parked for a while.

Pressures also tend to fall as temperatures drop, so the first cold snap of the season is a good moment to check them even if you did so recently.

Where to find the right pressures

The correct pressures for your car are usually on a sticker on the driver's door pillar or inside the fuel filler flap, and always in the vehicle handbook. Most cars list different figures for normal driving and for a fully loaded car, and front and rear pressures are often different. If you are heading off with a full boot, a roof box or a caravan on the back, use the loaded figures.

How to use a portable tyre inflator

A portable inflator lets you top up at home at the right moment – with tyres cold – rather than after driving to a forecourt. Most plug into the car's 12 V socket, while cordless models run from a rechargeable battery. The basic method is similar for most:

• Park on level ground, apply the handbrake and make sure you are safely clear of traffic.
• Check the inflator's instructions on whether the engine should be running. Many 12 V inflators draw a fair amount of power, so running the engine avoids draining the battery – but only do so where it is safe and appropriate, not in an enclosed garage.
• Remove the valve cap and screw or clip the inflator's connector firmly onto the valve.
• Read the current pressure. If your inflator has an auto-stop feature, set the target pressure from your door-pillar sticker or handbook.
• Inflate in short bursts if needed, and follow any guidance on rest periods, as some compact inflators should not run continuously for long.
• Disconnect, refit the valve cap and repeat on the other tyres, including the spare if you have one.

It is worth cross-checking the result with a separate pressure gauge now and then, so you know your inflator's readout agrees with it.

TPMS warning light on: what to do

Most modern cars have a tyre pressure monitoring system, or TPMS, which warns you if a tyre loses pressure. If the light comes on, find somewhere safe to stop and check all the tyres. If one is visibly low or losing air, do not keep driving on it. If the pressures are simply a little low, inflate them to the correct figures and follow the handbook, as some systems need to be reset after you adjust pressures.

If the light stays on or flashes even with correct pressures, the system itself may have a fault. That matters at the MOT: the MOT inspection manual lists a malfunctioning TPMS on vehicles first used on or after 1 January 2012 as a Major defect.

Other tyre points the MOT looks at

Beyond tread depth and TPMS, one detail catches some drivers out when replacing a single tyre: the MOT inspection manual lists mixing radial and cross-ply tyres on the same axle as a Major defect. Cross-ply tyres are uncommon on modern cars, but it is worth knowing if you run an older vehicle or a trailer. For a full run-through before your test, see our MOT preparation checklist.

What to keep in the car and garage

A basic tyre kit does not take up much room. Our tyre inflators collection covers portable inflators for topping up at home or on the road, and the tyre and wheel tools range covers tools for checking and working on tyres and wheels. For the tyres and wheels themselves, browse the tyres and wheels collection, and if you like to keep wheels and sidewalls clean, the tyre and wheel care range covers products for cleaning tyres and wheels. A weekly look at your pressures and a monthly tread check will tell you far more than any product can on its own.

Frequently asked questions

What is the legal minimum tyre tread depth in the UK?

For cars, the Highway Code says tyres must have at least 1.6 mm of tread across the central three-quarters of the breadth and around the entire circumference. Many drivers replace tyres before they reach this limit.

How often should I check my tyre pressures?

The Highway Code advises checking at least weekly, with the tyres cold. The correct figures are usually on the door pillar or fuel flap sticker and in the vehicle handbook.

What should I do if my TPMS light comes on?

Stop somewhere safe and check all the tyres. Inflate to the correct pressures and follow your handbook, as some systems need resetting; if the light stays on with correct pressures, have the system checked.

Can a faulty TPMS fail the MOT?

Yes. The MOT inspection manual lists a malfunctioning TPMS on vehicles first used on or after 1 January 2012 as a Major defect.

Should I check pressures before or after driving?

Before, or once the car has been parked for a while. Tyres warm up while driving, which raises the reading, so a check on hot tyres can be misleading.