How do I set my tyre pressures correctly?

Tyre pressure is the single cheapest thing that affects how a car stops, steers and how much fuel it uses, and it is also the thing most likely to be wrong. Tyres lose pressure slowly on their own, so a car that has not been checked for six months is almost certainly running soft.

Safety

What you'll need

• A pressure gauge, or a forecourt air machine
• The placard figures for your car
• A compressor or foot pump (optional)

Step by step

1. Find your car's figures, not the tyre's.The number moulded on the tyre sidewall is the tyre's maximum, not your car's recommendation. The correct figures are on a placard in the driver's door shut, inside the fuel filler flap, sometimes in the glovebox, and always in the handbook.
2. Note that there are usually two sets.One for normal use and one for a fully loaded car. Most people only ever use the first, which is why cars packed for a holiday so often feel vague and wallowy on the motorway.
3. Check the front and rear separately.They are frequently different, because the engine sits over one axle. Setting all four the same is a common and avoidable mistake.
4. Check when the tyres are cold.Cold means the car has stood for a couple of hours, or has driven less than about two miles. Warm air expands, so a hot tyre reads high and you end up letting out air the tyre needed.
5. Unscrew the valve cap and press the gauge on squarely.A brief hiss as it seats is normal. A continuous hiss means it is at an angle and the reading will be low — reseat it.
6. Add or release air in small amounts.Check again after each adjustment rather than trusting the machine's own display, which on a busy forecourt is often out.
7. Do the spare as well.A spare wheel that has been ignored for four years is usually flat, which is discovered at exactly the worst moment. Space savers often take a much higher pressure than the road wheels — check the label on the wheel itself.
8. Refit every valve cap.The cap is the seal that keeps dirt and water out of the valve. A missing cap is a slow puncture waiting to happen and costs pennies to replace.
9. Look at the tyres while you are there.Tread depth, cuts, bulges, anything embedded. Thirty seconds a tyre, and it is the check that finds problems before they find you.
10. Put a monthly reminder in your phone.Tyres lose roughly a pound or two of pressure a month with no fault at all, so a monthly check is not fussiness, it is just keeping up.

Tips

• Buy your own gauge. A decent one costs less than a tank of fuel and is far more accurate than most forecourt machines.
• If a dashboard tyre pressure warning appears, check all four with a gauge before assuming the system is wrong.
• Use the loaded figure for a holiday, and remember to put it back afterwards.

Common mistakes

• Using the number printed on the tyre sidewall — That is the tyre's maximum safe pressure, not the pressure your car was designed around. Setting to it makes the ride harsh, the grip worse and wears the centre of the tread out.
• Checking pressures after a long drive — Warm tyres read several pounds high. Letting air out to reach the placard figure leaves the tyre badly under-inflated once it cools.

If it doesn't work

Questions people ask