It's a heat issue.
The reason airlines and race car crews fill their tires with nitrogen has absolutelly nothing to do with rate-of-loss or oxidation or even fuel economy. Nitrogen expands and contracts at a lesser rate with changes in temperature than atmospheric air. The process of separating the nitrogen out for the tanks used in this process removes the moisture content in normal air. It is the presence of moisture that causes the noticable increase in tire pressure with temperature increase. This is a BIG deal when you cruise at 200mph for 500 laps and you need all the traction you can get (meaning keeping the pressure as low as regulations allow).
It makes a big difference on airlines for massive planes coming into land where tire temperatures skyrocket rapidly. Again, keeping expansion down gives the pilots better traction, hence better control, during the rollout.
Last edited by milo; 02-18-2008 at 11:38 PM.