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Originally Posted by livvie
What should really be addressed here is the moisture content that goes into your wheel when you fill up at an air pump.
If the air pump could filter out most of the moisture in the air, then you would NOT have drastic differences in PSI due to a hot/cold tire. I believe the nitrogen air pumps are devoid of any moisture content and that's a big reason why you don't see unpredictable PSI numbers given the temp of the tire.
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This is a good point. The water (moisture) content is the only thing that would effect how a tire pressure changes with temperature. The water may go from a liquid to gas (evaporate) when the tire heats up or gas to liquid (condense) when the tire cools down. The temperature-pressure profile would be different for a dry-filled tire versus a wet-filled tire. There should be no difference in the temperatue-pressure profile for a nitrogen filled tire versus an oxygen filled tire. They both remain gases over the entire operating conditions of the tire and both behave identically as ideal gases.
I notice that the website posted in this forum claims that nitrogen filled tires hold their pressures better because the molecular size of nitrogen is bigger than that of oxygen. The size difference is only about 5% and would not make a difference in leak rate of 3 to 4 times as the website claims. Most likely, there would not be a noticable difference.