Want Nitrogen With That?


Remember that great closing scene in The Bridges at Toko-Ri where admiral Tarrant, upon contemplating the loss of Brubaker, ruminates, “Where do we get such men?” For all the wrong reasons, I thought of that the other week when I was talking to Dave, one of the local IAs here.

While I was fooling with the plugs in the Cub, he said, “Hey, what do you know about nitrogen in airplane tires?” My reply is that I knew as much about it as I do nitrogen in car tires, which is enough to understand that using it is yet another way to separate a customer from his money.

This had come up because a customer had come into the shop asking to have the front tire on his Cessna 172—yes, a Skyhawk—inflated with nitrogen. When the shop said it couldn’t help, the customer steamed off in a hissy, muttering that the place must not know the first thing about maintenance.

But I had been around these houses before when the local Toyota dealer offered to “freshen” the nitrogen in our Matrix tires for $5 a pop. Did I want this special service? Not just no, but hell no. Twenty bucks to top up the tire pressures? I later learned that this was a bargain. Some dealers charge as much as $179 for this “upgrade.” The idea has somehow migrated over to airplane tires, but apparently via meme, not by anything the manufacturers recommend.

The theory behind nitrogen inflation is that it retains tire pressure over time better than straight air does and this has proven to be true. But we’re talking very small differences. Consumer Reports did a yearlong test and found that nitrogen held pressure in a tire about 1.3 PSI better than straight air. That’s in tubeless tires; it might be different in the tubed tires that light aircraft use. Nitrogen is typically drier than compressed air, so it’s also thought to reduce moisture content around the metal wheel, thus limiting corrosion. But again, in an airplane, the moisture is inside the tube and never sees the wheel surface. Nitrogen acolytes also believe that because the gas is inert, it will reduce tire degradation. Well, that’s fine, but the tire is exposed to all manner of destructive UV and environmental contamination on the outside, so what’s the point of protecting the inside with a $20 top off?

There isn’t one. Or at least one that’s consistent with spending that much on a tire you’ll probably replace long before a nitrogen fill will pay off. And since it’s an airplane, we’re not really worried about fuel economy.

It is true that transport category tires are nitrogen filled; says so right in the tire specs for those big, expensive buns. But that’s not what we’re talking about here. I didn’t speak to this owner directly, but I would have liked to. Isn’t flying expensive enough without, you know, doing it to ourselves? Ain’t it funny how we talk ourselves into such things?