How temperature changes tyre pressure

Air in a closed tyre follows temperature. A usable rule is 1 psi (about 0.07 bar) for every 5–6 °C, or roughly 1 psi per 10 °F. A drop from 15 °C to 0 °C can take 3 psi off a tyre that had no puncture.

The reverse is also true. A car set to placard on a 0 °C morning will read high on a 28 °C afternoon. Do not bleed that heat. The next frost will need the air you dumped.

Seasonal practice in Britain: check monthly, and extra after the first hard frost and the first heatwave. Set to the placard on a representative cold morning for that season.

Garage versus kerb matters. A car that lives in a 12 °C garage and then sits on the street overnight is not at the same starting temperature. Measure where the car actually soaks.

Nitrogen follows the same physics. Marketing that nitrogen “does not change with temperature” is false.