Although our atmosphere has around 20% O2, some tires have several atmosphere's worth of pressure in them. The partial-pressure of O2 is then greater than 100% O2 at atmospheric pressure. This can start to spontaneously combust things. Aircraft tires, which often have 8 to 9 Bar (atmospheres) of pressure in them all run nitrogen. Given a high enough partial pressure of O2, aluminum will burn.
Ever let the air out of a tire and smell it? Smells like rotten eggs... The 2 to 3 Bar of pressure in a tire brings the partial-pressure of O2 up high enough that it's oxidizing the rubber. Your tires are rotting from the inside out.
Most street vehicles don't have 200 PSI of pressure in them. But, Nitrogen (no O2) will keep your tires happier longer. Also, N2 (the gas) has a larger atomic radii than O2 or other trace gasses. This larger diameter allows membranes or semi-porus aluminum castings to hold the tire pressure without slowly leaking.
Just my 2 cents.