Well can't speak for F1, but certainly use nitrogen on my mates race car, much less pressure fluctuation between hot and cold pressures. With air we were inflating to about 20 psi cold for a hot pressure of about 30 psi. Reduced down to about 25 psi for a hot pressure of 30 psi with nitrogen. we do have to deal with contaminants though, as trundling around a nitrogen cylinder to club racing events is not seen as terribly good form <img src="wink.gif" border="0"> , so mionr adjustments are made with air. In fact we just popped down to a Halfords garage, where they will purge and replace with dry nitrogen for £1 a tyre