Tires Inflated With Nitrogen Investigated

At Costco's 4 metro tire centers, the air is always out. That's because they inflate with pure nitrogen. Costco says it's a clear advantage.

They convert the air into nitrogen, right in the store.

Inside, the machine separates out the oxygen, leaving only nitrogen behind. The nitrogen then goes into a holding tank, until it's time to pump up the volume on a set of tires.

Because nitrogen molecules are larger than oxygen, they seep out of tires more slowly.

And that is the key behind claims that you can get better gas mileage -- riding on nitrogen.

We couldn't find any study that backs up that claim, but the Department of Energy says correct tire pressure and alignment can help save you 3% on gas.

Of course, when your tires pressure does fall -- you have to go back to the tire shop to re-inflate them with nitrogen.

Maria O'Neil of Lilburn doesn't mind. She bought nitrogen tires for her son's car, and when her vehicle needs them, she plans to get them right here

“I drive an Excursion and it gets horrible gas mileage, so anything that's going to help get better gas mileage, I'm for.”

Of course, you can just use regular air, which is almost 80 percent nitrogen -- and check your tire pressure more often.

The one upside confirmed by the government: Your tires will last longer if you have 100 percent nitrogen in them.