N2 expands as much as any gas mixture in the quantities, temps, and pressures we care about here.

PV = nRT. Its called the universal gas law for a reason.

Molecule size has negligible effect on 'leakage' through tire 'pores'.

Its the water that makes the difference. N2 is pumped in"dry" as in no moisture coming out of the bottle. THAT is the only advantage. You could get the same effect using an air dryer/dessicant tower with regular air if you got the dewpoint low enough.

There have been threads about this before-
http://www.greenhybrid.com/discuss/n...light=nitrogen

http://www.greenhybrid.com/discuss/n...light=nitrogen

http://www.greenhybrid.com/discuss/n...light=nitrogen