Their is Nitrogen naturally occurring in air. It is true the Nitrogen won't do it's job as well with air in there, but it is still better than straight air. Nitrogen and air just mix to create a% solution heavy in Nitrogen. You don't need to bleed off the Nitrogen then fill with air.

I've run air in my tires for years with no issues at all....and it's free.

 

I made sure that was true. I used the mileage * pumped gallons and got my mpg. It was right around what I posted. As for why not to use air and nitrogen mixed, I'll scan the brochure about the nitrogen when I go back up to get them refilled.

 

Normal atmosphere is 78% Nitrogen. So ALL CARS have nitrogen-filled tires.

If you are managing tire pressures like a Formula One team you will see advantages in the more predictable thermal properties of pure nitrogen.

Pure Nitrogen will not reduce rolling resistance, prevent blowouts, improve gas mileage or stop global warming.

Just Plain Keeping your tires properly inflated will do that.

A google search will reveal that the only people telling us about the advantages of nitrogen in street tires is are the people selling (wait for it) nitrogen tire inflation systems.

Cecil Adams is not sold on the advantages:

http://www.straightdope.com/columns/...instead-of-air

Nor are the Tappet Brothers:

http://www.cartalk.com/content/colum...bruary/02.html

Bottom line: keeping the tires properly filled with good old Air is probably your best bet for better gas mileage.