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.

You then go to the station and top your tires off with air to bring them back to the proper pressure.  Now you have almost all nitrogen in the tire that you added a small amount of air to.  At that point you would have much less oxygen in the tire than you did when you first inflated it.

Assuming that the oxygen continues to leave the tire and the nitrogen remains you would have an even higher percentage of nitrogen in your tires.  Maybe 95%.  As you repeated this over and over you would eventually have nothing but nitrogen in your tire.

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 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.

Once again there are those who are taking advantage of a situation to make a buck.  Who finds an advantage to filling tires up with nitrogen?  Those selling the equipment and those retailing the nitrogen. They earn more profits.  Who gets the short end of the stick?  That’ right, it’s the consumer.