Hate to be the bearer if bad news but N2 in conventional tyres is a complete waste of time (apart from the fact that good ol' air in almost 80% N2) - great way for tyre retailers to make some extra money though.
If however, you live in a very humid climate, conventional unfiltered air may have a lot of water in it which when condensing, evaporating or freezing (whatever the case may be) will result in pressure changes (which is one of the reasons commercial jets have N2 in their tyres). You could also argue that "pure" nitrogen does not have very much oxygen or water in it and being relatively inert does not react with the tyres, although I haven't heard of too many tyre failures caused by the rubber tyre compounds reacting/oxidising with air. With regard to pressure changes - pure air (no water) and N2 probably are both as close to an 'ideal' gas as each other and hence have same P to T ratios.
bikeless no longer! welcome home, 2011 KTM 990 Adventure!