I think my tires threw osmosis have about 90-95% nitrogen in them now !
I own my own own small tank air pump , I think i should start selling nitrogen fills , $1 a tire for 79% at first 90-95% over time I will offer them the Math as proof , as we suspect oxygen leaks out faster at the same pressure.. Money to made that's for sure !
Remember Air has only 20% oxygen meaning there can only be a possible 20% difference in air loss time , but should be more like 5-10% when compared to to the small percent of difference in oxygen amount mathematically.
from link
The Reality
In 2007 Consumer Reports published a comparison of air-inflated tires and nitrogen-inflated tires to see how fast each type lost pressure (article here). It was a pretty thorough test, involving 31 different models of automotive tire inflated to an inital pressure of 30 psi, with the loss of pressure measured over a period of one year. Detailed results are shown in a spreadsheet, but what it all boils down to is that on average the air filled tires lost 3.5 psi, and the nitrogen-filled tires lost 2.2 psi. 3.5 divided by 2.2 equals a leakage rate for air that is 1.59 times as great as nitrogen. That's remarkably close to what the theory predicts.
If you check out that spreadsheet (see link, previous paragraph), you'll notice there's a wide variation in pressure loss from tire model to tire model. Some tires lost a fraction of a psi, while the BF Goodrich tire lost around 7 psi. So if your buddy notices his new nitrogen-filled tires are hardly losing pressure at all, ask him if they're the same brand as his old tires. There may also be a difference in leakage rates between brand new tires and tires that have racked up thousands of miles.
Nitrogen for Tires: Question #4