How weather affects tyre pressure

The ever-changing UK weather doesn't only influence your mood and BBQ plans. It will also alter the air pressure in your car's tyres which, in turn, can affect your vehicle's road holding, steering performance, braking distance, all-round safety and fuel economy. Not to mention how long your tyres will last and remain in good condition.

Tyres are essentially tubes of reinforced rubber filled with pressurised air. Like any gas, the air in your tyres is subject to the laws of physics. Warmth increases pressure and cold makes it lower.

Other factors can also affect your tyre pressure, such as friction from the road surface generating heat. But the main cause of changing tyre pressure is the ambient temperature—in other words, the weather.

But how much of a difference does the weather make? As a rule of thumb, every 10°C rise or fall in temperature affects a tyre’s pressure by between 1 and 2 PSI. So, the change in your tyre pressure from summer to winter can be up to a 15% difference. It's enough to affect the way your tyres and vehicle perform.

Resistance and friction cause a build-up of heat inside car tyres.. The warming effect of the weather then adds further pressure.

However, most tyres are engineered with built-in air pressure tolerances. Unless conditions are very extreme, you should be able to drive in hot weather without changing the tyre pressure—as long as you keep monitoring it and watch out for signs of overheating.

Bear in mind that the tyre pressure recommended by the vehicle manufacturer is set for cold conditions, so tyres should always be inflated in the shade, and never while the vehicle is still warm from driving.

Tyre materials and their black colour make them good at absorbing heat. Consequently, if they're hot to the touch, that means they're close to overheating. It's time to stop driving and let the tyres cool off. The hotter the tyre, the higher the pressure, so letting some air out may seem like a good way of dealing with overheated tyres, but beware. It could mean your tyres are underinflated when their temperature returns to normal.

When your tyre pressure is too high, it can significantly increase the risk of a blowout. Also, less of the tread is in contact with the road, reducing traction. You're less safe as a result, and you'll notice less responsive handling while driving. Our guide to over inflated tyres provides a more in depth look into the affects.

If your car has been sitting in low temperatures for any length of time, the tyre pressure is likely to have dropped significantly. The "0.19 PSI for every degree Celsius" rule applies in cold as well as heat. This pressure drop is likely to be compounded by natural leakage, as air slowly escapes.

Tyres with low pressure can become damaged and wear out more quickly, which can increase the likelihood of punctures. Low pressure also makes tyres heavier, which causes greater rolling resistance when driving. This can harm braking performance—increasing your stopping distance by up to four car lengths in wet conditions. It can also increase fuel consumption—because the engine has to work harder to drive the wheels.

At Halfords, we recommend monthly tyre pressure checks in all weather conditions, even if you're doing little or no driving. As well as using a tyre pressure gauge and reinflating as required, inspect the tyres for damage. That will help to nip problems in the bud before they become serious, or even dangerous. You'll find our simple guide to checking and inflating tyres here.

Most modern vehicles have a built-in tyre pressure monitoring system (TPMS). You can read all about this in our Halfords TPMS guide, but in brief, its function is to warn you if one or more tyres’ pressure is too low. TPMS is not always completely reliable and it won't alert you if the pressure is too high, so check your tyre pressure with a gauge as well. Better still, head to your nearest Halfords and we'll check it for you.