I really believe that tires losing pressure is a result of factors OTHER than using plain air as opposed to nitrogen. For those that feel nitrogen was better, did they used nitrogen on the same exact tires that were losing air before on regular air, and now don't lose air, or they switch to nitrogen after changing to new tires?

I feel that most air is probably lost from very very very slow leaking from the rim/tire joint. Then second is possibly from the valve itself. Third is probably from the manufacturing of the tire itself. I have always just used plain air, and I've only had maybe three or four tires that would lose air faster than 5 lbs. in one month. Other than those, I either never even had to refill within a year or they lost at most maybe 2 or three lbs every four or five months. Surely not sufficient to me to justify using nitrogen.