Nitrogen is generally used when pressurising tyres because there is less moisture in it, this also means that there is less fluctuation in pressures between hold & cold.
If you fill your tyre up with normal compressed air cold, then go and drive it around until it has warmed up, you’ll notice a significant difference between the two pressures.
Nitrogen is used in tyres to avoid air leaking through the tyre wall, which results in under-inflation. The reason why nitrogen is used is because it is easy to produce, does not support combustion, has no smell and is also a component of atmospheric air.
The difference between the pressure in a tyre and the pressure outside causes oxygen to permeate through the tyre. If we can create the same concentration of oxygen inside and outside tyre (equal partial pressure) then oxygen is not forced to leak through the tyre wall. Using nitrogen in tyres maintains the correct pressure, and reduces all the problems associated with under-inflation.