Nitrogen isn't for weight. It's not for fires.
You fill your tires with nitrogen because there's no water vapor in it... temperature changes don't affect your tire pressure nearly as much, and the carcass lasts longer.
Dangit, you beat me to it.
Additional Gee Whiz: They use in aircraft tires because of the extreme temperatures that it faces and how water vapor would increase wear and blow out the tires. Example, you are up there in a jet flying around. It's freakin cold up there, and the water vapor inside the tires condenses, lowering your tire pressure. You go to land, and your tires hit that runway and they instantly heat up a whole lot, espcially when you brake. The condensed water in the tire with low pressure, now becomes steam inside of a tire with high pressure. Not really good for the tire. Do that enough and your tire will prematurely wear out compared to if it had just had pure nitrogen in it.
I think it's bullshit to pay money to get your tires filled with nitrogen...isn't oxygen something like 78% nitrogen anyway?
I would love to see your chemical formula. N
39O
11