Originally Posted by bike2math
This morning there was a sidebar on NPR about people filling their car tires with Nitrogen (alla Nascar as mentioned above) I forget the reference but they said that the cost was about 2-5 $ per tire, and that the savings added up to 1 m/ga.
This sounds absurd. 1 mpg improvement would be a 4 to 10% improvement in the mileage depending the car. Come on, this can't be serious.
Air is about 80% Nitrogen already and the physical properties of most gasses (certainly Oxygen and Nitrogen) at typical pressures and temperatures are nearly identical so there should be no demonstrable difference in compressibility or anything else. It sounds like NPR got suckered into doing a free ad for the Nitrogen sellers. If I could get $2-5 per tire, I'd lie too.
BTW, the problem with CO2 isn't it's "weight". It diffuses through the inner tube faster than air, apparently due to greater solubility in the rubber, so the tires lose pressure faster.