snip

If the brakes are never used then the brakes won't add heat. Unless the
area of the wheel exposed to the filling gas is a fair proportion of the
area of the sidewalls then I can't see much heat going out the wheels
regardless of the gas used. Are you sure there is a large area of wheel
surface exposed anyway?

I haven't seen a racing tire up close and personal but if they are like
most other tires the bead/s run pretty close from side to side and it
doesn't appear that there is much metal not covered by rubber in most
wheels.

I have done a fair amount of measurements of tire temperature and heating
using IR sensors in the wheel wells under racing conditions. The data was
recorded with a data aquisition unit during racing, and downloaded to a
laptop between races. We did 10 sample per second, with 1 degree resolution.
I can state with confidence that a large portion of the tire cooling is due
to airblast on the tire carcass. The percentage of cooling by the metal
wheel is a very small fraction of the total heat dissipation.

Going a step further, with certain high end racers, the inner safety liner
completely insulates the metal wheel from the fill gas and tire face. This
does not seem to affect the heat balance in any measureable way.

Anyway, I don't buy the "runs cooler" argument for nitrogen any more
than anyone should buy the "nitrogen expands less" nonsense.

I am not sure what you have taken from this thread. Conventional wisdom is
that the measured pressure increase is due to liquid water flashing to steam
above the boiling point of water. It has nothing to do with the fraction of
oxygen or nitrogen in the fill gas. In the turns NASCAR and F1 cars run peak
tire temperatures between 225 and 250 degrees F. I leave it to you to offer
an alternate explanation of the measured 4 to 16 PSI jump (nominal 30 PSI)
under racing conditions. This increase is enough to completely scuttle
chassis tuning. While you are at it, explain how switching from running
"air" to dry nitrogen combined with a few forced purge-fill cycles
eliminates the effect - the tires pressure changes pretty much as predicted
by PV/T = PV/T.

This stuff is not conjecture - it is measured data. If it does not match
your expectations - perhaps it is time to reexamine your expectations.

Mark Browne