In an ordinary street car, nitrogen in the tires is pretty much useless snake oil. The air you breathe and use to fill your tires at the gas station is I believe 82% nitrogen.
"Nitrous" = Nitrous oxide = laughing gas at the dentist office = oxygen booster when injected into an engine. Nitrogen = largest component of Earth atmosphere and when used at higher concentrations to fill a tire provides somewhat better resistance to leakage due to larger molecular size and more temperature / pressure stability. Checking your tire pressure regularly and adjusting it accordingly achieves the same goal. Some tire chains "nitronize" your tires for free. I wouldn't pay for it, though.
