On this page
- Why does pressure drop when it is cold?
- Why does the warning light come on in the morning and then go off?
- Cold or a leak: how can you tell the difference?
- How should you manage tyre pressure in autumn and winter?
- Is it dangerous to drive on tyres that have gone down in the cold?
- Flat tyre on a cold morning in Milan?
- Frequently asked questions
Why does pressure drop when it is cold?
Pressure drops when it is cold because a gas sealed in an almost constant volume, like the air in a tyre, loses pressure as the temperature falls. It is a normal physical phenomenon, not a fault with the tyre.
The drop is gradual and affects all the wheels in the same way. As a rough guide, the drop is estimated at about 0.1 bar for every 10 °C fall in temperature: a swing of a few tens of degrees between summer and winter is enough to take the tyres below the correct value.
Why does the warning light come on in the morning and then go off?
The light comes on in the morning because, after a cold night, the pressure is at its lowest and can fall below the TPMS threshold. As you drive, the tyre warms up, the pressure rises again and on some systems the light goes off.
That is no reason to ignore it: it means the tyres are already at the lower limit. Check and restore the pressure. To find out what to do when the light comes on, read the guide on the tyre pressure warning light.
Cold or a leak: how can you tell the difference?
Cold lowers the pressure in a similar way on all the wheels; a leak, on the other hand, usually affects just one tyre and comes back after you have inflated it.
| Sign | Probably the cold | Probably a leak |
|---|---|---|
| Which wheels | All of them, more or less equally | Just one, or one much more than the others |
| After inflating | The pressure stays stable | It drops again over the following days |
| When it happens | With the first cold spell, in the morning | In any season |
If you suspect a leak, read slow puncture: how to find the hole and check the valve too.
How should you manage tyre pressure in autumn and winter?
In autumn and winter the pressure should be checked more often, always with the tyres cold, and brought back to the value given by the manufacturer.
- Check the pressure at the first sharp drop in temperature.
- Measure in the morning or after a long stop, before driving.
- Inflate to the value on the door pillar label or in the manual (see where to find the correct pressure).
- If you swap your summer tyres for winter ones, check the pressure on the newly fitted tyres too.
If you inflate in a warm place (a heated garage) and the car then stays outside in freezing weather, the pressure will drop further: bear this in mind.
Is it dangerous to drive on tyres that have gone down in the cold?
Driving on tyres that are slightly under-inflated is not an immediate emergency, but over time it reduces grip and braking, increases fuel consumption and wears the tread shoulders.
In winter, with cold and often wet roads, grip matters even more. A tyre that is very low, on the other hand, should be treated as a genuine tyre losing air: do not keep driving on it for long.
Flat tyre on a cold morning in Milan?
If you find a tyre completely flat one morning, the cold alone is unlikely to explain it: a leak is more likely. Do not drive on the flat tyre.
In Milan and its province, SOS Tyre comes out 24/7, in 30 minutes on average, even outside your home or in your garage: we get you back on the road in no time. Call +39 377 326 0999 or fill in the request for assistance.
Frequently asked questions
Should I inflate my tyres more in winter?
Not beyond the manufacturer's value: you simply need to bring them back to that value, because the cold makes it drop. Always measure with the tyres cold. Some manufacturers give specific guidance for winter tyres: check the owner's manual.
Do tyres lose pressure overnight in a garage too?
If the garage is heated or at least less cold than outside, the drop is smaller. But if the car goes from a mild garage into freezing weather outside, the pressure drops during the day. The reference remains a cold measurement, in the conditions the car is usually in.
Does the pressure rise in summer with the heat?
Yes, pressure increases with heat, just as it increases while driving. But do not let air out of hot tyres to bring them back to the value on the label: always measure and correct with the tyres cold, otherwise once they cool down they would be under-inflated.
I have inflated the tyres but the warning light stays on: why?
Some TPMS systems, especially indirect ones, need a reset after the pressure has been restored; others go off by themselves after a short drive. If the light stays on or flashes, check the manual: you may need to carry out the reset procedure or have a sensor checked.