Do nitrogen-filled tires maintain proper pressure longer? The premise for this claim is that nitrogen is a larger molecule than oxygen. It is. Only slightly. But let’s not omit the fact that we’re talking about molecules here and not just the element. Oxygen and nitrogen are both diatomic molecules. Nitrogen actually has less mass than oxygen, so Graham’s Law dictates that it diffuses a bit faster than oxygen. However, since the actual size of the oxygen molecule (O2) is a bit larger than that of a nitrogen molecule (N2), this only applies if the opening from which the molecules are effusing from is large enough to permit the largest of the two. In such cases, N2 will diffuse faster. The question, then, becomes, are the pores in rubber (assuming there are such pores) smaller than the N2 molecule but larger than the O2 molecule? I don’t know the answer to this. Nor could I find any literature in the few minutes I searched, but if anyone has a citation to an independent (i.e. non Nitrogen Tire industry) study or bit of research, I’m interested. Without digging out my old chemistry textbook, I’m willing to tentatively accept Wiki Answers on the sizes of N2 and O2 molecules: N2 is roughly 300 picometers while O2 is slightly smaller at 292 picometers. I’m open to revising these figures if someone cites a more reliable source, but I can’t imagine that there’d be any reason for the link to be more than slightly wrong. Does rubber oxidize faster when exposed to oxygen rather than pure nitrogen? I’d expect so. The real questions are: a) how to you keep oxygen on the outside of your tires from causing oxidation?, and does it really matter to me since every single tire I’ve ever replaced was because of worn tread and not oxidation I see the moisture issue if you have a problem with wheels rusting out. I have never seen this happen. Ever. I have no proof that nitgrogen tires hold air better in fact you can scew numbers to point either way. It is a scam in my opinion and I wont sell it. Am I losing money maybe but I wont sell something I dont believe in.