Originally Posted by
prathmann
When people just refer to 'tire pressure' it's implied that they mean 'gauge pressure' since that's the quantity that matters, that's what we measure with our pumps or pressure gauges, and that's what varies when we go up in altitude or load our bikes on airplanes
+1
Gauge pressure, or the difference between inside and outside pressure will change, and the change is equal to change in external pressure. While chemists are concerned with absolute pressure, the mechanical considerations will depend on gauge pressure, which is what we measure.
Referencing
this chart we see a drop of about 2.5psi between sea level and 5,000' altitude. So the
gauge pressure in a tire will increase by that amount, which is trivial in the scheme of things.
Even if we put the bike into an unpressurized aircraft and take it up to 40,000' we'd only get an increase of about 12psi, well within the working tolerance for tire pressure.