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.
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 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 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.