Originally Posted by unfoundhorsepower
Nitrogen is an inert gas....very stable, what it does for tires is: The pressure does not fluctuate much at all from hot to cold, It is very stable and does not promote tire oxidation, internally...many owners of restored cars fill their tires with it for long term storage....10 years... Does anybody who drives their car all the time need it ???NO...a waste of $$$$$$$...It DOES NOT help to keep your tires inflated any longer than regular air does, on a daily basis.
That's a misconception.
The tire pressure DOES fluctuate from hot to cold with pure nitrogen, and it's much more than "not much at all." The advertisement gimmick is that the amount pure nitrogen fluctuates is less than that of air, but air is nearly 4/5's nitrogen as it is...
To put it in perspective, Nitrogen is an ideal gas. For ideal gasses, PV=nRT. P = Pressure in Pascals, V = Volume in cubic meters, n = number of moles, R = 8.314 (gas constant), and T is temperature in Kelvin.
To compare an ideal gas pressure at two different temperatures, the V, n, and R cancel out and leave P/T = P/T.
80* F = 26.7* C = 299.81 Kelvin
38 PSI = 262000 Pascals (Pa).
So lets say the temperature falls to 40*F on a cold night. That's 4.4* C = 277.6 Kelvin.
Punch that into the P/T = P/T equation and you your new pressure is 242590 Pa, which is roughly 35 PSI.