Why Put Nitrogen in Tires, Especially in Winter

Posted Friday, Dec 07, 2018

As we enter cold weather, you may notice your tires become a bit slack (to avoid this, people put Nitrogen in tires). That’s because the ambient air that was pumped into your tires contains nitrogen, oxygen, carbon dioxide, water vapor, and various other trace compounds. It’s a well known fact that gases contract as they cool, and the water vapor exacerbates this phenomenon. So, that ambient air in your tires contracts when cold and hence has less pressure in the winter. The only way to know how much the pressure has lessened, you'll have to check with a tire pressure gauge. If you've never checked tire pressure before, you can read a "How To" article here: How to Check Tire Pressure and Inflate/Deflate Accordingly.

However, if you have nitrogen pumped into your tires, this low pressure occurrence will hardly happen. First of all, nitrogen won’t seep through your tires' rubber compound as easily as will oxygen.* Since atmospheric air is 21% oxygen, almost ¼ of the air in your tire can migrate through the rubber itself. It's odd to think, but the tire is porous enough for oxygen molecules to slowly find a way out. Additionally, nitrogen is very insensitive to temperature; hence its pressure hardly fluctuates with temperature changes. Lastly, nitrogen (which has been filtered) will be pumped directly from a tank into your tires with no water vapor, so you’ll not have that compound to condense and lower pressure (or rust your wheels). Incidentally, if a tire is below its recommended pressure, its sidewalls will flex more than they were designed to; this compromises the sidewall resulting in even faster permeation of oxygen- sort of like a "snowball effect." Since Nitrogen offers less chance for you to accidentally drive on under inflated tires, it also lessens the chance of the tire allowing more leaking. So, it may be worthwhile for you to consider putting nitrogen in tires.

Photo courtesy reasonablerides.com

*The reason that O2 permeates through rubber more easily than N2 is because the O2 molecule is smaller. This seems counter-intuitive since Nitrogen is #7 on the periodic chart while Oxygen is #8. However, because an O2 molecule has 16 protons in the two nuclei, there is a greater attraction between the two nuclei and the electrons thus reducing the diameter of the electron cloud to a greater degree than N2's 14 protons in its two nuclei. Think of it like this: an O2 molecule and a N2 molecule are shaped like pills, but the O2 "pill" is slightly smaller- it's easier for the tiny pores in the tire to swallow the O2 "pills." In fact, O2 permeates through 3-4 times as fast as Nitrogen.