I have seen car dealers that tried to sell you on filling the tires with nitrogen for an extra $500 or whatever. Which makes me think, first off, how the heck would I know that was worthwhile, and then secondly, if they'd scam you in the first place, how do you know they actually even put any nitrogen in the tires? And how do they get the air out first? if the "empty" tire is full of air, then you inflate with nitrogen, about 30% of what's in there is still the original air which didn't go away.