ok, so if the air we breathe is 78% nitrogen, then after X period of time, the smaller molecules, 22% (for the sake of argument) will leak out before the nitrogen, correct?
to keep things simple lets imagine that there are 100 air molecules in the tire, 22 of which are non-nitrogen that will leak out faster
this leaves the tire 78% inflated
a properly maintained vehicle will have the tires checked and filled regulary, so that the tire will get topped off with another 22 molecules to fill the void left by the assumed smaller than nitrogen molecules, with my calculations this would add roughly 17 nitrogen molecules and 5 misc others. thus after one tire pressure check and refill, the tire will contain the origional 78 molecules plus the new 17, totalling 95, or 95% nitrogen
this 95% is probably just as much as a tire filled with nitrogen will have due to the initial space in the tire filled with ambient air before inflation.
Therefore, i hope no one pays extra for something that can be accomplished through one pressure top-off
2002 Nissan Maxima SE - 15.143 at 91.74mph - Short Ram Intake - 2* Timing Advance- Tein Coilovers - Front Strut Brace
00-01 SE Tails - Smoked side markers - Painted and Cleared Headlights - Weathertech rainguards - Tinted to 27% - CF Gauge Trim
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2000 Bonneville SE - Retired