Originally Posted by stlwagon
Well, military aircraft use nitrogen in most tires. Nitrogen molecules are larger than air and escape less rapidly and it is also less susceptible to expansion and contraction. Nitrogen is also lighter than air and people have reported better gas mileage. It isn't cheap. Can cost a few dollars per tire to fill.
Actually, Nitrogen isn't any less susceptable to expansion and contraction than any other pure
gas. Pv=nRT for all pure gasses.
The benefit (aside from the already mentioned lack of seepage due to a larger molecular size) is that Nitrogen, unlike air, does not have any water vapor in it. It is the water vapor in regular air that is chiefly responsible for the increases/decreases in pressure caused by varying temperatures. Even the tiny bit of water vapor in normal air has a huge impact on pressures as temperature varies. If you were able to fill a tire with normal air at 0% humidity, it would respond to pressure in the same way the pure Nitrogen does. However, air, even at 0% humidity, would still leak out more easily.
Personally, it's cheaper for me to just use my compressor and keep an eye on my pressures. On the other hand, I can easily see it being worth the money to someone who doesn't want to adjust their tire pressure every week.
Claims of increased mileage are faulty, and are either the result of new tires (most people switch over when new tires are fitted) or of having had the tires under-inflated before switcing to Nitrogen. Claims of a smoother ride likewise baffle me since X PSI is X PSI regardless of the particular gas creating the pressure and Nitrogen at 32 PSI will cause the tire to behave exactly the same as if it were inflated with air at 32 PSI.