I've always checked my tires warm. Is this not the more accurate and real world way to do it ?
As jmarshal replied, Tire Pressures are specified at 'cold' or ambient temps.
Two reasons: - People are more likely to check and adjust pressures before they head out, rather than after driving for a while. Also, driving conditions can increase tire temps considerably, and pressure as a result.
As pressure increases with temperature, the same starting pressure could have significantly different pressures after a long highway run, vs a short spin to the gas station air pump. How can anyone know if their tires are hot enough to give the correct 'warm tire' pressure if that was how the tire companies had chosen to specify them?
In winter tire temps & pressures may not rise much at all. If you don't compensate for the lower ambient winter temps your tires will run under-inflated.
More accurate to specify cold pressure specs for tires to more accurately get the correct starting point pressure for the ambient temps of that season.
Gary