[CapriRacer]

Just so we are all on the same page:

The point of the test is to simulate the heat buildup in a tire and see how that impacts the pressure buildup. Oilpan4 says he doesn't expect much, but he never explained why. I suspect it is because the Ideal Gas Law is a pretty good way to predict pressure buildup.

But the one thing that jumped out at me when I reviewed the posts in this thread was that using the sun to simulate the heat buildup in a tire was somewhat non-analogous. That is, the heat in the air chamber of a tire comes from the hysteretic properties of the tire components (mostly the rubber) and that is not uniform around the perimeter of the tire. The tread will generate more heat than the sidewalls because the tread has much more material that is being moved.

And I think the point of using a different gas in a tire (ala F1) was to move that heat away from the tread area to an area where it could dissipate - like the sidewall. The net effect would be to slow the heat buildup internally to the tire, and to speed the cooling down. In F1, this would help preserve the tires, plus allow the driver to push for a longer period, then have less time to cool the tires down before having another go at fast laps.