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 big claim made by nitrogen believers is that nitrogen will save gas by keeping your tires at the optimum pressure level. They suggest that nitrogen permeates from your tires slower than oxygen. The pressure loss of the tire is less over time because the nitrogen is staying in the tire 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.

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.

If this were the case, that the oxygen leaves the tire while the nitrogen is left behind, you would eventually end up with nitrogen filled tires. All the while just filling them with air. Since you now have nitrogen filled tires why on earth would you fill your tires with nitrogen to begin with and spend the extra money?

This is just a common sense answer as to why the claims of nitrogen being a significant factor in reducing gas consumption just don't hold up. There many more specific scientific answers as to why the nitrogen claims are false. Most of them are way to complicated to try and explain in one short article. In the end it seems you are seeing the one law of physics that seems to manifest itself over and over.

As is generally the case there are those who always take advantage of some problem to make a profit. Who gets the benefit of filling your tires with nitrogen? Non other than the manufacturers of the nitrogen producing equipment and the merchants who sell the nitrogen to the public. They make more money. Who ends up paying for those extra profits? That' right, it's you.