Originally Posted by SSE Motorhead
Nitrogen still obeys the ideal gas law. Therefore it will not maintain a constant pressure as the tire heats up - that is to say the pressure at 20* will be less than the pressure at 100*.
Yes, it does obey the ideal gas law, so it will change it'* pressure over temp.
However, it obeys the ideal gas law a lot better than compressed air with water vapor in it (which isn't an ideal gas at all.) You call water vapor negligable, I dissagree. There is a heck of a lot of moisture inside a tire filled with compressed air...which is exactly why they don't fill aircraft and race tires with it.
As a matter of history, the aircraft industry adopted it first in the 1950'* as more aircraft became equiped with high pressure tires for use on paved runways. Most of the aircraft from the 1940'* were equiped with ballon tires that worked on unimproved runways and took up a lot of space inside the aircraft. Problem, when you take a tire and fill it with compressed air at 120 degrees, then take it up to 30,000 feet where the temp is about as zero as zero can get...it goes flat. Bring it back down from altitude..it will stay flat until it warms back up..which will probably be after you try to land on it..Ooops! Corrosion on the wheels is a mixed bag...a lot of aircraft tires are still equiped with tubes, so corrosion of the rim isn't much of an issue.
Nitrogen works and is worthwhile on a race tire is that contour of the tire is important to the way it handles (even more so on a motorcycle race tire, where a few psi change in pressure can make major handling differences in the bike.) A race tire is also subject to drastic heat changes on a road course...stuff you would never see on a street tire.
On a street car, it is a waste of money.