Cold and hot tyre pressure.
A tyre checked after a run reads high, and bleeding it down to the placard figure leaves it under-inflated once it cools.
What this assumes
- The tyre is a fixed volume and no air is added or let out. Close enough for a mounted tyre on a rim.
- The calculation is done in absolute pressure, not gauge pressure. This is the step done wrong by hand: scaling a gauge reading directly overstates the rise by roughly a third at normal car pressures, because the gauge does not count the atmosphere already pressing on the outside.
- Temperature is the temperature of the air inside the tyre, which after a run is hotter than the air around the vehicle.
- Cold means the tyre has stood for a few hours out of the sun, not that the weather is cold. Set pressures cold, and check them against the placard on the door pillar or in the handbook - never against a figure from a calculator.