The greatest benefit of nitrogen tire inflation compared to standard compressed air—or the type of air you’d typically find at the air pump at your local gas station—is that nitrogen may help keep tires inflated longer. It’s a matter of basic chemistry. Standard compressed air is composed of the same air we breathe. This means it’s about 78% nitrogen, 21% oxygen, and 1% a mixture of other gasses such as carbon dioxide. Compressed nitrogen for tire inflation is much more homogenous, generally between 93-99% pure nitrogen with the rest comprised of an admixture of other gasses.
Nitrogen molecules are larger than oxygen molecules, meaning that it’s more difficult for nitrogen to leak out of your tires through the inner liner membrane used to retain air. This natural process of air escaping is known as permeability. While both nitrogen and oxygen can and will eventually find their way through the tire’s inner liner, it can take up to six times longer for nitrogen verses oxygen.
Also, the compressed air in your tires contains water vapor, just like the air we breathe —this is what’s called humidity. In tires, this water vapor has two effects. First, it can accelerate the oxidation process. Secondly, water vapor pressure varies a lot with changes in temperature. This can result in increases (or decreases) in your tires’ pressure. Compressed nitrogen in tires, on the other hand, is dry, making it more stable than standard compressed air, even at the higher temperatures tires are subject to at highway speeds.