The purpose, I've been told and it may be pure BS, of Nitrogen in tires, which works out to about 92-96% if the tires are filled properly, it to reduce the percentage of Oxygen in the tires.
Oxygen is a component of water. The higher percentage of oxygen, the greater chance of moisture in the tire. Nitrogen isn't a component of water. Moisture in the tire increase breakdown of tire components slightly. More importantly, most commercial air stations don't provide 'dry' air. The moisture content varies.
Nitrogen doesn't migrate through the rubber tire walls as easily as oxygen. It doesn't expand or change pressure nearly as much as oxygen. Race cars use nitrogen to control tire pressures within 1/2 pound of pressure. Something that is impossible with normal air.
That said - I firmly of the belief that for the type of driving we do with current vehicles, RVs and such - Nitrogen is worth about 1/2 cents per tire over the life of a tire.
So on a cost / benefit ratio - I don't bother with finding pure nitrogen. Regular air is good enough for me.
