On this page
- Why should pressure be checked when the tyres are cold?
- How do you check tyre pressure, step by step?
- How often should you check tyre pressure?
- Petrol station gauge or your own?
- If I have TPMS, do I still need to check the pressure?
- What should you do if one tyre is much lower than the others?
- Frequently asked questions
Why should pressure be checked when the tyres are cold?
Pressure should be checked cold because, while you drive, the tyre heats up and the air inside it expands: the reading comes out higher than the actual reference pressure.
The values given by the manufacturer refer to cold tyres. If you measure after a long drive, you risk thinking the pressure is correct when in fact, once the tyre has cooled, it is low. For the same reason, never let air out of a hot tyre to bring it back to the value on the label.
How do you check tyre pressure, step by step?
To check the pressure you need a gauge (or a compressor with a gauge) and the manufacturer's value.
- Find the correct pressure for your car and your load: read what your tyre pressure should be.
- Unscrew the valve cap and put it somewhere safe.
- Press the gauge head firmly onto the valve so that no air escapes.
- Read the value and compare it with the reference.
- If it is low, inflate in small steps and check again; if it is high (when cold), let a little air out by pressing the valve pin.
- Put the cap back on: it protects the valve from dirt and moisture.
- Repeat on all four wheels and, if you have one, on the spare wheel.
How often should you check tyre pressure?
Many vehicle and tyre manufacturers recommend checking the pressure at least once a month, as well as on certain specific occasions.
- Before a long journey or when the car is loaded.
- When temperatures drop noticeably, for example at the start of autumn: see why tyres lose pressure in the cold.
- After an impact with a pothole or kerb.
- When the TPMS warning light comes on or the car seems to pull to one side.
A tyre naturally loses a little pressure over time even without any holes: regular checks are there precisely to correct this drop.
Petrol station gauge or your own?
Both are fine as long as they are reliable, but your own gauge lets you always measure with cold tyres and with the same instrument.
| Petrol station gauge / air line | Your own gauge | |
|---|---|---|
| Cold tyres | Often not: you get there after driving | Yes, you can measure at home with the car parked |
| Accuracy | Variable, depends on maintenance | Consistent, if the instrument is good quality |
| Inflation | Yes | No, you need a compressor |
If you measure at the petrol station after a few kilometres, bear in mind that the tyre is slightly warm: avoid letting air out and check again when cold as soon as you can.
If I have TPMS, do I still need to check the pressure?
Yes: the tyre pressure monitoring system (TPMS) warns you of a drop beyond a certain threshold, but it does not replace regular checks with a gauge.
Indirect TPMS in particular compares the wheels with each other and may not notice an even drop across all four. To understand how the warning light works and what to do when it comes on, read the guide on the tyre pressure warning light.
What should you do if one tyre is much lower than the others?
If one tyre is much lower than the others, there is probably a leak: a nail, a small hole, the valve or the bead on the wheel rim. Pumping it up may be enough for a short while, but the problem comes back.
Look at the tread for foreign objects and read the pages on a tyre losing air and a nail in the tyre. In Milan and its province, SOS Tyre comes out 24/7, in 30 minutes on average, to wherever the car is, even outside your home: call +39 377 326 0999.
Frequently asked questions
How long does the car need to be parked for the tyres to be cold?
A few hours parked is usually enough, for example in the morning before you set off. If you have to measure after driving, do so after only a few kilometres at low speed. The further you drive, the more the tyre heats up and the higher the reading compared with the actual cold value.
Does the valve cap really matter?
Yes. The cap protects the valve's internal mechanism from dust, sand and moisture, which over time can make it leak. It is not what holds the air in, but a dirty valve can leak: always put it back after checking and replace it if you lose it.
Can I trust the compressor in the repair kit?
The emergency kit compressor usually has a built-in gauge that is useful for inflating, but its accuracy varies. It is fine in an emergency; for regular checks, a dedicated, reliable gauge is better, always used with the tyres cold.
Do I need to check the spare wheel pressure too?
Yes. A flat spare wheel or space-saver is no use when you need it. Check them during your regular checks, using the pressure specified by the manufacturer, which for the space-saver is often different from that of the normal wheels.