Tyre pressure FAQ
What pressure should my tyres be?
Use the tyre-information placard on the driver’s door pillar, measured cold. Catalogue pages show a general band in PSI, bar and kPa. The sidewall number is a maximum, not the target.
How do I convert bar to PSI?
Multiply bar by 14.5038. 2.4 bar ≈ 35 psi. 2.5 bar ≈ 36 psi. Divide PSI by 14.5 to get bar. 100 kPa equals 1 bar.
Why are there separate front and rear pages?
Many vans, estates and performance cars print two numbers. Front tyres steer (and often drive); rears take payload. Copying one axle onto the other is a common mistake.
When is a tyre cold?
After the car has stood at least three hours, or been driven less than about a mile. Do not bleed pressure after a motorway run.
Does temperature change the gauge?
About 1 psi (0.07 bar) per 5–6 °C. A UK frost can light TPMS without a puncture.
Is the sidewall the safe number?
No. That is the tyre’s maximum. Running a family hatch at 51 psi because the flank says so wears the centre rib.
What about plus-size wheels?
Start from the vehicle placard, keep load index at or above original, and do not drop pressure to soften a low-profile tyre. Size tables on model pages are estimates.
When does TPMS warn?
Direct systems typically light around 25% below the placard. That is already low. Fill to the sticker.
Space-saver spare?
Often about 60 psi / 4.1 bar. Read that tyre’s own sidewall. Speed and distance limits still apply.
How often should I check?
Monthly, before a long trip, and after a large temperature swing. Include a full-size spare.