Originally Posted by milo
It's a heat issue.
Nitrogen expands and contracts at a lesser rate with changes in temperature than atmospheric air.
There would be NO change in internal tire pressure due to a decrease in atmospheric pressure. There would be a slight increase in the DIFFERENCE between internal and external pressure due to the fact that atmospheric pressure would be less at altitude, but even this would most likely be more than offset due to the drastic drop in temperature that occurs at higher altitudes. As far as using Nitrogen to control pressure on aircraft tires it very well could make a difference on landing with all that heat build-up and the point about the moisture content in regular compressed air makes a lot of sense.