Bob wrote:  I wonder if you guys in the US use
nitrogen?

The appeal of nitrogen is that the source (bottled nitrogen) is dry,
virtually all moisture out of it.  Consequently tires filled with
nitrogen tend to run cooler.
As far as nitrogen not expanding or contracting with temperature, it
behaves like any other gas but with all the moisture out heat will be
neither absorbed nor retained like it is with regular air.  And BTW, the
air you are breathing is 78% nitrogen.
One of the problems in using nitrogen is purging the air already in the
tire.  Easy to do, break the bead, flood with nitrogen to purge (push
out) the air, reseat the bead, and inflate to desired pressure.