Here's an interesting excerpt from an article regarding using nitrogen in tires:
The earths atmosphere is composed primarily of Nitrogen (78%), the remaining balance is a mixture of Oxygen (21%) and a small percentage of Ozone, Argon and Carbon gases. Isn’t it ironic that the very gas (oxygen) that sustains life also causes organic materials to decompose and metals to rust?
Remove The Oxygen And Stop The Rot
To stop this decomposition you simply need to remove the oxygen from the ‘air’. (Incidentally, removing oxygen also means that you remove water because water is two parts Hydrogen gas, and one part Oxygen gas.)
Removing Oxygen from products is not new, we do it all the time with our food and drink. In fact, if we did not remove the oxygen our food would not likely last long enough to make it into the hands of the consumers – or it would taste stale and unappealing.
Nitrogen In Tires
Here are a few other benefits of using Nitrogen in tires:
 Nitrogen is denser than Oxygen: This means the larger molecules escape less easily from tires resulting in a more gradual loss of pressure over time. According to the Michelin Tire Manual, a tire that is inflated with Nitrogen loses its pressure 3 times slower than if it were inflated with air.
 Nitrogen is moisture free: Pure Nitrogen inflated tires experience less steel belt and rubber degradation. Nitrogen use also reduces valve and wheel corrosion.
 Nitrogen provides longer tire life: Nitrogen inflated tire run cooler and require less maintenance according to the Goodyear application bulletin.
 Nitrogen is non-flammable: Nitrogen technology has been used in aircraft, military and race car technology for over thirty years.
Hopefully this will help clear up some of the myths.