Dear Mr. Magliozzi,
I have read many responses to the question of the effectiveness of nitrogen in preventing the loss of gas in tires. Here is my angle on this issue: Since the air we breathe is approximately 78% nitrogen and 21% oxygen the tire starts out with 21% oxygen at one atmosphere pressure (14.7 psia) when the tire is place on the rim. Then when the tire pressure is increased to 3 or 3.5 atmospheres (30 - 37 psig or 45-52 psia) with pure nitrogen, there still is the initial amount of oxygen in the tire, so as a percentage there is 7% oxygen in the tire at 30 psig. A tire would need to be mounted in a 100% nitrogen enclosure to end up with 100% nitrogen which is impractical to do.
Please feel free to edit my comment.
Thanks for a great job
Mike Shebel, The Villages, Fl