) states that the pressure of a gas is inversely proportional to the volume. Doesn't matter what gas it is, they all behave the same way. Charle's Law(http://en.wikipedia.org/wiki/Charles%27s_law
) states that the temperature of a gas is proportional to the volume of the gas, again, it doesn't matter what the gas composition is, air and nitrogen behave the same way. That's phsyics.
Consumer Reports looked at nitrogen: http://blogs.consumerreports.org/car...nitrogen-.html
Popular Mechanics: http://www.popularmechanics.com/cars...stions/4302788
How Stuff Works: http://auto.howstuffworks.com/question594.htm
And Commercial Fleet Digest: http://www.psitiredigest.com/tiredigestjuly07.pdf
Professional race cars experience temperature swings much higher than passenger cars, and the articles mentioned the effect of water vapor present in air that is responsible for the difference. Most of the tire manufacturers won't endorse nitrogen as no one has shown a proven benefit.
Stick with air, and check it regularly.