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Good Question: Does Nitrogen Help Fuel Efficiency?

MINNEAPOLIS (WCCO) -- With skyrocketing gas prices, some say carpooling and biking may not be the only ways to lessen the pain of paying at the pump. They recommend nitrogen in tires.

Debbie from Forest Lake e-mailed us to ask: Does filling our tires with nitrogen improve fuel efficiency? Good Question.

"It's becoming more frequent," said Costco manager and former Tire Center employee Chuck Henning. "Most places it's common now."

Costco was one of the first companies on the nitrogen bandwagon, offering free nitrogen fill-ups with the purchase of tires.

"The benefit of nitrogen is the consistent pressure, whereas if you're rolling on an under-inflated tire, it creates more rolling resistance, thus leading to a lower gas mileage," Henning said.

Henning says nitrogen helps to keep the PSI (pounds per square inch) more constant in the event of a temperature change.

"For every ten degrees that the air temperature changes, you would lose one pound of air pressure," Henning said. He argues with nitrogen, the PSI is constant.

We went to the Physics Department at Hamline University in St. Paul, where longtime professor Jerry Artz sees things differently.

Artz says the atmosphere is already 78 percent nitrogen to begin with and the rest is mostly oxygen. The oxygen that's in the air, which we fill our tires with, is actually helpful, he says.

Oxygen has a higher molecular mass than nitrogen. Artz says this is important because more massive molecules mean slower movement -- thus it won't diffuse through the tire's cracks as quickly.

In other words, he says, the dry air is going to stay in the tires longer than a nitrogen concentrate. Artz also says both oxygen and nitrogen react the same to temperature changes.

The one benefit to nitrogen, and the reason you see nitrogen used in airplanes and race cars, is because there's less water vapor. The more water vapor, the more corrosion on metal surfaces.

One thing's for certain: the best thing you can do for your tires is to check the inflation pressure once a month.

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