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.
Basic chemistry and physics supply the answer. First, take a deep breath, hold it for a second, now let it out. Did you know the air you just inhaled was 78% nitrogen? Certainly you could tell that when you inhaled, couldn't you. That is the biggest myth buster of all in considering nitrogen versus air. Nitrogen already composes 78% of air. Only 21% of air is oxygen.
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.
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.
You then go to the station and top off your tires which are now filled with a high concentration of nitrogen. You add a small amount of air to the tire. Now you have much less oxygen in the tire than you did when you first inflated it. It has a much higher 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.
Based on the claim that oxygen would leave the tire faster, you would end up with nitrogen filled tires while filling them with air. If this were the case then what would be the point of filling your tires with nitrogen to begin with?
This is just a plain logical example as to how false the nitrogen claims are. There of course are a myriad of specific scientific answers showing why the nitrogen claims are based on myths and not scientific facts. Each one would require a separate article in itself to explain. In the end it seems you are seeing the single law of behavior that seems to play 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.
Scott Siegel is the author of a 143 page manual of automotive industry insider secrets on saving gas and dollars at the pump (beatthegaspump.com). Visit us to learn how you can get better gas mileage. Find out how to increase gas mileage.
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