There is a spreading belief that if you put Nitrogen (instead of regular air) in your car tires, that you will get better gas mileage. The reasoning behind this may be sound, but the facts on which the reasoning is based are not correct. Therefore, the answer is no, it is not advantageous for the average person to use Nitrogen in their car tires. On even more detailed examination, it maybe that regular air is better than Nitrogen for most people. Nitrogen is in fact used in certain tires, and there may be a good reason for that, though the information I have is probably missing something. In other words, it is all rather complicated. The short answer is, don’t bother with the Nitrogen, but there are some interesting details:
First, note that Nitrogen (from a Nitrogen tank) is all Nitrogen, while “air” is about 78 percent Nitrogen, with the rest being mostly Oxygen but also some other stuff including a variable amount of water vapor. In certain specialized uses, such as in airplane tires, Nitrogen is preferred because it lacks the water vapor, and thus, contributes less to corrosion of metal parts. I suspect there may be more to it than that, but the point is, using pure Nitrogen from a compressed Nitrogen tank means a pure gas and thus whatever other issues one might have with regular air would be obviated.
The argument for using Nitrogen in your car tires is this: Air and NItrogen would compress at different rates depending on temperature, with air being more squishy than Nitrogen, and that would cause your tires’ pressure to vary more with air than with Nitrogen. Indeed, having more variation in tire pressure is bad because there is one ideal pressure; more variation means that the tires will be at the idea pressure less often. The idea that air and Nitrogen compress differently is predicated on the assumption that Nitrogen has a single and more ideal compression dynamic than air.
However, this is probably mostly not true. Air is mostly Nitrogen, the rest of the air is mostly Oxygen, and Oxygen and Nitrogen have about the same dynamics with respect to compression and density and stuff, according to Physicist Jerry Artz.
Now, since I’m a skeptical skeptic, and not just a skeptic, I’m going to suggest that even though all this is true it is quite possible, in fact likely, that the water vapor in “air” is much more dynamic in terms of pressure than Nitrogen or Oxygen, and thus, variation in pressure of the tire contents based on temperature may be measurable if there is enough water vapor in there. I’m thinking this is most likely why Nitrogen is used in certain tires. That is, however, merely a hypothesis at the moment. I’m offering this guess because I think it unlikely that corrosion is a question in racing car tires, yet racing teams often use Nitrogen. Anybody out there know the answer to that one?
So, on one hand, the suggestion that Nitrogen is better than Mostly Nitrogen and Stuff Like Nitrogen and a little bit of other stuff mixed together is probably very much over stated. Yet, the idea that pure Nitrogen and randomly sampled air are exactly the same is highly unlikely. Having said that, the degree of difference between “air” and Nitrogen is probably not great.
And, most important of all: If you want to make the air pressure in your car’s tires ideal, the elemental and molecular composition of the gas you put in there is far, far less important than the process of checking your tire pressure regularly (i.e., weekly) and maintaining it. The variation over weeks of time from minor leakage (and there is minor leakage in a perfectly good tire with a perfectly working valve) is greater, probably, than the difference between Nitrogen and air.1
Which brings us to the final and possibly most important point: Nitrogen can sneak out of the leaks more easily than Oxygen, according to Professor Artz. Therefore, filling your car tires with regular air then ignoring them, which is what you actually going to do, is better than having Nitrogen put in there at your local service shop or Wallmarts, then ignoring them.
And, really, there is a better way to save on gas: Get a more efficient car and drive less.
1Also, while you are checking the air in your tires every week, could you also please drain your hot water tank annually and check with a physician before starting a new exercise program? Thank you very much.
Drawing of Nitrogen from Wikipedia.