By Russ and Tiña De Maris
If you remember high school chemistry, you may remember our friend nitrogen, the gas that makes up the majority of earth’s atmosphere. While “plain old air” has been used for years to fill tires, the wrinkle a few years back was to fill tires subjected to a lot of stress with nitrogen. Think race car tires, jet aircraft, etcetera. Why nitrogen?
Plain old “oxygen” molecules are about one-fourth the size of nitrogen. Because of that, rubber tires slowly “leak” air because the rubber is a bit permeable – the air slowly works its way through the tire pores, if you will. Since the nitrogen molecules are so much bigger, tires tend to lose pressure far more slowly. As a result, the tires run cooler and get better fuel economy. Sounds like “N-inflation” is a shoe-in? Hang on, might it lead to a false sense of security? If you don’t check your tire pressure as often, will you likewise fail to look your tires over for damage?
Tire permeation isn’t the only reducer of tire pressure. Witness a statement from tire maker Michelin: “The existence of several other possible sources of leaks (tire/rim interface, valve, valve/rim interface and the wheel) prevents the guarantee of better pressure maintenance for individuals using nitrogen inflation.” The company does not recommend nitrogen inflation, except “in a high risk environment and/or when the user wants to reduce the consequences of a potential abnormal overheating of the tire-wheel assembly (for example in some aircraft applications).”
Notwithstanding, economics may come into play. A nitrogen tire “fill up” can cost you as much as $10 each. If you’re somewhere where nitrogen is unavailable and have a low tire, you can “top off” the tire with ordinary air. But later you’ll be advised to have the tire bled out and refilled with nitrogen.
Revision note: A correction from “air” to “oxygen” related to size of molecules made. 4/7/18 12:38PM MST