How to check tire pressure (and find the right figure)

Checking your tire pressure (tyre pressure in the UK) is one of the easiest and most useful jobs you can do on a car. Correct pressures help the car brake and steer as it should, and make the tires last longer.

Find the right pressure first

Look for the recommended pressure in one of these places:

• A sticker inside the driver's door jamb. The most common spot.
• Inside the fuel filler flap, on some cars.
• Your owner's manual.

The figure is given in psi, bar or both (1 bar is about 14.5 psi). Many cars list different pressures for the front and rear tires, and a second, higher figure for when the car is fully loaded. For most passenger cars the normal figure is around 30 to 35 psi (about 2.1 to 2.4 bar), but always use your car's own number.

Do not use the number on the tire sidewall. That is the tire's maximum pressure, not the pressure your car needs.

Why check them cold

Driving warms the tires and the air inside them, which raises the pressure. The recommended figures are for cold tires, so a reading taken after a drive will look higher than it really is. Tires count as cold when the car has been parked for at least two to three hours, or driven only a short distance at low speed, less than about 1 miles1.6 km.

If you have to check hot tires, for example at a gas station on a trip, expect them to read about 4 to 5 psi (0.3 bar) higher than the door-sticker figure. Do not let air out to bring them down: top up only if they are below the recommended pressure plus that margin, and recheck when cold.

Step by step

1. Park on level ground with cold tires, and switch off the engine.
2. Find the recommended pressure on the door jamb sticker or in your owner's manual. Note the front and rear figures.
3. Unscrew the valve cap on the first tire and put it somewhere safe.
4. Press the gauge firmly onto the valve until the hissing stops, then read the pressure.
5. Add air if it is low. Use a gas station air pump or a portable tire inflator, adding a little at a time and rechecking with the gauge.
6. Let air out if it is too high by pressing the small pin in the center of the valve in short bursts, rechecking as you go.
7. Refit the valve cap. It keeps dirt and moisture out of the valve.
8. Repeat on all four tires, and on the spare if your car has one.

If a tire keeps losing air

A tire that is low again within days probably has a slow puncture, a leaking valve or a damaged rim. Have a tire shop look at it. If a tire is visibly flat, has a bulge on the sidewall, or the car pulls or feels unstable, do not drive on it: fit the spare or call for help. If the tire pressure warning light comes on while you are driving, check all four tires at the next safe stop.

How to keep it simple

• Check once a month and before long trips, ideally first thing in the morning.
• Check again when the weather turns cold: pressure drops by about 1 psi for every 10°F (about 6°C) fall in temperature.
• Raise the pressures to the full-load figure before a trip with a heavy load or passengers in every seat.
• Keep a gauge in the glovebox.