[QUOTE="Nasty"] Is this where I say "Duh!"? <It includes water vapor and Yes it does. That's why it's CALLED the other 24%. I think you just solidified my case. If somebody wants to go off the deep end and do something extravagant filling their tires there's always helium. It's inert, resists temperature changes well, and should make the car go faster because of its lift characteristics. Then again too small a car with too large tires my tend to float. But that could be kinda cool too... Again, YMMV.[/QUOTE] no kidding. helium diffuses through rubber like you left the door open. fact is, unless you have a specific [aerospace type] need such as corrosion resistance, condensation resistance or fire resistance, an all-nitrogen tire inflation is utterly pointless.