OK OK, the official Gas Man checking in again!!!
Were not talkin about Nitrous Oxide. Nitrogen gas. Or get the liquid and you'll get more from a small container. You get liquid Nitrogen and when you open the container it expands into a gas/vapor state. This is similar to your propane on your grills.
Nitrogen is NOT flammable and can even be vented into the atmosphere without any worry from the EPA. I know, because we use Nitrogen all the time at work for many reasons.
The Nitrogen should act very similar to air as you are rolling on it. Nitrogen expends when heated, therefor causing increased pressure. Just as your standard air does in your tires. My only worry is the likelyness of it to expand when heated from the sun beating on the tire in a parking lot. Our nitrogen tanks at work do this all the time and "blow off" the excess pressure thru a pressure relief valve.
I'm not saying it's a good thing for the tires but intresting anyway.