Nitrogen for tires

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

Hi, not Ray but a frequent commenter on this forum.

I agree with your analysis and that is what happens in practice at tire shops that use nitrogen. They SHOULD fill and purge the tire a few times to flush out most of the oxygen but I’ve never seen one do that.

The reason for nitrogen is to inflate the tire with a dry gas with no moisture in it. A well maintained compressor with water trap will do that without the need for nitrogen fill. The last few tire changes I’ve had were with nitrogen fill. As long as it is free, I am OK with it but not if I must pay for it.