Originally Posted by Chu Chu
"if the oxygen was diffusing faster, it wasn't by much. And when you consider that air is only 20% oxygen to start with, a slight decrease in the diffusion rate for that 20% isn't going to make much difference in tire pressure."
According to a 2009 NHTSA study, the inflation pressure loss for tires inflated with nitrogen was approximately two-thirds of the loss rate of tires inflated with air. They tested both static and in-use automotive tires.
"The Effects of Varying the Levels of Nitrogen in the Inflation Gas of Tires on Laboratory Test Performance" (4.6MB .pdf):
http://tinyurl.com/jvcgfxo