Busting the Nitrogen Saves Gas Myth

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 the most basic principle of all. Take a deep breath. Now let it out. You realize that the breath you took was 78% nitrogen. I'll bet you couldn't tell. Therein lies the biggest problem with the theory that nitrogen is better than air. Air is already 78% nitrogen!

A major claim made by nitrogen advocates is that nitrogen is a larger molecule and will permeate through the tire slower than oxygen. By slowing the seepage out of the tire, nitrogen will allow you to maintain the proper pressure in the tire longer.

The natural laws of physics don't support that contention. The rate of seepage of a gas through a porous membrane depends on it's mass and on it's size. Nitrogen and oxygen are almost the same size and nitrogen is slightly lighter than oxygen. If either gas is going to seep through the tire then the nitrogen would actually seep slightly faster than the oxygen.

Think about this for a minute. If oxygen actually permeated out of a tire faster than nitrogen, then as the tire deflated what would be left in the tire would be mostly nitrogen. Let's say there was 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 train of thought, if the nitrogen does continue to behave the same way, the smaller amount of oxygen now in the tire escapes from the tire and the nitrogen that remains behind becomes even more concentrated. Maybe you now have 95% nitrogen in your tires. As you continually repeat this process many times, you continue to get higher and higher concentrations of nitrogen in your tires. Eventually you will end up with 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.

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Scott Siegel is the author of a 143 page book of automotive industry insider information on saving gas and money at the pump (beatthegaspump.com). Visit us to discover how you can get better gas mileage. Find out how to increase gas mileage.
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