Nitrogen as an alternative to air when filling tires seems to be gaining some popularity. The fact that Costco and other retailers are now offering nitrogen fills certainly points to nitrogen filled tires as becoming more mainstream. At almost $10 per tire does it really save fuel like it is claimed to do? Here are some answers.

Let's start with a basic principle. Inhale...., now let it out. The breath you just took was 78% nitrogen. Of course you could tell that when you took that breath, couldn't you. That is the biggest problem with the assertion that nitrogen is better than air. 78% of the air is already nitrogen!

The basic claim made by nitrogen supporters is that nitrogen will permeate through the tire slower than oxygen because it is a larger molecule. By slowing the pressure loss of the tire, nitrogen will allow your tires to maintain the proper pressure longer.

This contention is just not supported by the laws of physics. The rate of diffusion of a gas through a porous substance depends on the mass and the size of the molecules of that gas. Oxygen and nitrogen are almost the same size and in fact nitrogen is lighter than oxygen. That means that if either is going to permeate through the tire the nitrogen would actually permeate faster than the oxygen.

Consider this little bit of common logic. If oxygen did indeed permeate through a tire at a faster rate than nitrogen, then as the tire lost pressure mostly nitrogen would then be left in the tire. Let's assume at this point there is 90% nitrogen left in the tire.

Now in order to bring your tire back to the proper pressure, you top off your tires with a small amount of air. You have in effect added a small amount of air which is 78% nitrogen to the residual air in the tire which is 91% nitrogen. The end result is your tire is now filled with an air mixture with a very high concentration of nitrogen.

Continuing this scenario, as it is claimed, the oxygen continues to dissipate from the tire and the nitrogen remains behind. Now you have an even higher amount of nitrogen in your tire. Maybe 95%. As you repeat this process again and again your tire would eventually end up being full of only nitrogen.

The question is, if eventually you would end up with nitrogen filled tires by just repeatedly filling them with air, why would you fill them with nitrogen to begin with and spend the more money? It just doesn't make sense.

This claim of nitrogen permeating out of a tire slower than oxygen has been shown to be false just by using a little logic and common sense. There are a lot of specific laws and formulas of physics illustrating why claims of nitrogen's benefits are false. They would take many articles to explain. Really though it seems the law you are actually observing is the single most common law of behavior that is repeated over and over.

Once again there are those who take advantage of a problem to make a profit. To whom is there an advantage to filling tires up with nitrogen? The companies selling the nitrogen producing equipment and the retailers who sell the nitrogen itself. They make more profits. Who comes out with the short end of the stick? That' right, it's you and me.