nitrogen

I was just thinking about nitrogen. They put it in tires, suppose to improve gas mileage, if normal air is already 80% nitrogen, what's the point? If the atmosphere is 80% nitrogen, how can Dick Rice say there is 90% humidity? Laughing gas is nitrogen, looks like we'd be laughing most of the time. If you look it up on the internet, it says when you crack your knuckles, it's nitrogen bubbles popping, I aint sure I buy that. Some web sites advertise that you can improve your MPG on your car by 2 miles per gallon just by replacing the air with nitrogen, yea right. If that were the case, all the manufacturers would put it in the tires straight off the assembly line to help meet their EPA numbers. I think I'll set up a shop and start putting Helium in tires, make the car lighter, that would improve gas mileage, then we can take all that nitrogen and get a good laugh.