Tyre pressure is the cheapest, fastest maintenance job on a car, and the one most often got wrong — usually because people read the number on the tyre instead of the number for their vehicle.
The sidewall number is not your target pressure
The figure moulded into the tyre sidewall — something like "MAX PRESS 350 kPa (51 PSI)" — is the maximum the tyre may safely be inflated to. It has nothing to do with what your car needs. Inflating to it will give you a harsh ride, a narrow contact patch, rapid centre wear and reduced grip.
Where the correct figure lives
- The door shut placard. Open the driver's door and look at the B-pillar or the edge of the door itself.
- The fuel filler flap. Common on VW Group and several others.
- The glovebox lid or the handbook.
The placard usually lists more than one figure — typically a "normal" or "comfort" pressure for light loads, and a "full load" pressure for a car carrying passengers and luggage. Front and rear are often different. Use the right column for what you are actually doing.
Check them cold
Pressure rises as tyres heat up — typically 3 to 5 PSI on a motorway run. "Cold" means the car has been stationary for at least three hours, or driven less than about two miles. If you have to check warm, do not bleed air out to reach the placard figure; you will end up badly under-inflated once they cool.
What under- and over-inflation actually do
Under-inflated
- Shoulders wear out prematurely while the centre stays fine.
- Rolling resistance rises — measurably more fuel or less range.
- Sidewalls flex and build heat. This is the mechanism behind most tyre failures at speed.
- Steering feels vague and braking distances increase.
Over-inflated
- Centre of the tread wears out early.
- Smaller contact patch — less grip, particularly in the wet.
- Harsher ride and more vulnerability to pothole damage.
How often?
Once a month, and before any long journey. It takes three minutes. Also check after the first properly cold snap of the year — a 15°C drop in ambient temperature will take roughly 3 PSI out of every tyre.
What TPMS does and does not tell you
Tyre pressure monitoring has been mandatory on new cars sold in the EU and UK since November 2014. There are two kinds:
- Direct TPMS uses a sensor in each wheel and can report actual pressures. Sensor batteries last roughly 5–10 years and the sensors are replaceable.
- Indirect TPMS infers pressure loss from wheel speed differences via the ABS sensors. It is cheaper, has nothing to replace, and needs resetting after any pressure adjustment.
Either way, TPMS is a warning system, not a substitute for a gauge. Most systems will not alert you until a tyre is around 25% below target — by which point you have already lost fuel economy and tread life. A faulty or non-functioning TPMS is also an MOT failure on vehicles first used from 1 January 2012.
Do not forget the spare
If you have one, check it. A spare that has been sitting at 12 PSI for four years is not a spare. Space-savers usually require a notably higher pressure than the road tyres — commonly around 60 PSI — so check the label on the wheel itself.