What Tyre Pressure Should My Car Be?

There isn't a single correct tyre pressure that applies to every car. The right pressure depends on your specific vehicle, the tyre size fitted, and sometimes how many people are in the car. Here is how to find the right figure for your car and why getting it right matters more than most drivers realise.

Where to Find Your Car's Correct Tyre Pressure

Every car manufacturer specifies the correct tyre pressure for that vehicle. You'll find it in three places: on a sticker inside the driver's door jamb (the most convenient), in the owner's manual, and sometimes on the inside of the fuel filler flap. The sticker is the most reliable source because it's specific to your car's exact specification.

The figure is given in PSI (pounds per square inch) or bar. Both are correct — they're just different units. 30 PSI is approximately 2.07 bar. Most UK tyre gauges show both scales.

Many cars specify different pressures for front and rear tyres. This is normal — the weight distribution of the car determines the correct pressure for each axle. Never assume front and rear are the same without checking.

What Happens When Tyre Pressure Is Wrong

Under-inflation is the more common problem and the more damaging one. When a tyre is under-inflated, the sidewalls flex more than they should with every rotation. That flexing generates heat, and heat is the primary cause of tyre failure. An under-inflated tyre running at motorway speeds is at genuine risk of a blowout — not immediately, but over time as the heat builds.

The wear pattern is also distinctive. An under-inflated tyre wears on both outer edges while the centre of the tread remains relatively intact. If you see this pattern on your tyres, low pressure is the most likely cause — though it's worth having the pressure checked rather than assuming, because the same pattern can sometimes indicate a suspension problem.

Over-inflation causes the opposite wear pattern: the centre of the tread wears faster than the edges. An over-inflated tyre has a smaller contact patch with the road, which reduces grip and makes the ride noticeably harsher. The tyre also becomes more vulnerable to impact damage — hitting a pothole at speed on an over-inflated tyre is more likely to cause a pinch flat or internal damage than the same impact on a correctly inflated tyre.

The fuel consumption effect is real but often overstated. Under-inflated tyres do increase rolling resistance, which increases fuel consumption — typically by 0.5–1% per 3 PSI below the recommended pressure. That's measurable over a full year of driving but not dramatic on a single tank.

The TPMS Warning Light

Cars manufactured after November 2014 are required by law to have a Tyre Pressure Monitoring System (TPMS). The warning light — a cross-section of a tyre with an exclamation mark — illuminates when one or more tyres drops 25% or more below the recommended pressure.

The important thing to understand is that 25% below recommended is already a significant problem. If your recommended pressure is 32 PSI, the light won't come on until you're at approximately 24 PSI. That's well into the danger zone. The TPMS light is a warning that something is seriously wrong, not a gentle reminder to top up.

TPMS sensors are battery-powered and have a lifespan of approximately 5–7 years. When the sensor battery fails, the light illuminates permanently — not because the tyre is flat, but because the system has lost the ability to monitor. A TPMS warning light that stays on after you've checked and corrected the pressure usually means a sensor needs replacing.

How Often to Check Tyre Pressure

Once a month is the standard recommendation, and it's a reasonable one. Tyres naturally lose approximately 1–2 PSI per month through normal permeation — the slow migration of air molecules through the rubber. That rate increases in cold weather, which is why pressures often drop noticeably in autumn.

Check pressure when the tyres are cold — meaning the car has been stationary for at least three hours, or driven less than two miles at low speed. Driving heats the air inside the tyre, which increases pressure. Checking a hot tyre will give you a reading approximately 4–6 PSI higher than the cold pressure, which will lead you to believe the tyre is correctly inflated when it may not be.

Before a long motorway journey, check all four tyres and the spare. Some manufacturers specify a higher pressure for fully loaded driving — this is usually noted on the door jamb sticker alongside the standard pressure.

Nitrogen vs Air

Some garages offer nitrogen inflation as a premium service. The argument is that nitrogen molecules are larger than oxygen molecules, so they permeate through the tyre more slowly, maintaining pressure for longer.

The science is correct. The practical difference for a passenger car is minimal. Nitrogen-filled tyres lose pressure approximately 30–40% more slowly than air-filled tyres — which means instead of losing 1–2 PSI per month, you lose approximately 0.6–1.4 PSI per month. For a car that's checked monthly, this makes no meaningful difference to tyre wear or safety.

Nitrogen is worth considering for track use, where tyre temperatures are much higher and pressure consistency matters more. For everyday road driving, regular monthly checks with standard air achieve the same result.

When to Have Pressure Checked Professionally

If your TPMS light comes on and the pressure appears correct when you check it, the sensor itself may be faulty. A professional check will identify whether the issue is a slow puncture, a faulty valve, or a sensor that needs replacing.

Slow punctures are more common than most drivers realise. A nail or screw embedded in the tread can cause a tyre to lose 2–3 PSI per week — slow enough that the TPMS light doesn't trigger immediately, but fast enough that the tyre is noticeably soft within a fortnight. If you find yourself topping up the same tyre repeatedly, it almost certainly has a slow puncture that needs professional attention.

Checking Pressure at a Petrol Station

Petrol station air pumps are convenient but not always accurate. The gauges on forecourt pumps are frequently uncalibrated and can read 2–4 PSI high or low. If you're using a forecourt pump, use it to add air rather than to measure — set the pressure slightly higher than your target and then verify with a quality handheld gauge.

A decent digital tyre pressure gauge costs £10–£15 and will give you a consistent, accurate reading every time. It's one of the most cost-effective car maintenance tools you can own, given that it helps you avoid the tyre wear and fuel consumption costs of running at the wrong pressure.