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Under Pressure

Before hitting the road this summer, you might take a page from the president's campaign playbook and make sure your tires really are properly inflated.

The American Automobile Association consistently finds that a fifth of all vehicles have at least one under-inflated tire. That may be because motorists are three times more likely to give their cars a monthly wash than a tire check. As a result, the U.S. Department of Energy reports that such under-inflation causes a loss of some 2 million gallons of fuel per day. But proper inflation isn't just a matter of fuel economy and tire longevity — under-inflation can also cause deadly blowouts.

Instead of sidling up to the nearest air hose, why not consider pumping them full of nitrogen instead?

Nitrogen already makes up a whopping 78 percent of the atmosphere. But because nitrogen molecules are larger than oxygen molecules, they are slower to leak through your tires' outer carcass.

Thus, nitrogen can maintain tire pressure an estimated four to six times longer than ordinary compressed air. The practical benefits are disputed, and Consumer Reports, which did a yearlong real-world test of nitrogen tires, found the difference smaller than that "four to six times" figure but still real. Another study conducted for the Canadian government (by an official of a company whose product line includes nitrogen-inflation equipment) found a 3.3 percent fuel savings, all things being equal.

Aircraft, military vehicles, racecars, off-road mining and construction vehicles, motorcycles, commercial trucking fleets and even a few Tour de France bicycles have been using nitrogen-filled tires for years. Today, ordinary motorists are gradually making the switch to nitrogen as well.

The Colorado-based Get Nitrogen Institute reports that more than 13,000 auto and tire dealerships sell nitrogen to some 15 million consumers in North America alone. By their calculations, if the average driver switched to nitrogen-filled tires, they could save well over a hundred dollars a year in improved gas mileage and increased tire life.

To foster that end, for the past five years, the Massachusetts-based Parker Hannifin Corporation has marketed a line of commercial nitrogen generators that run off existing air compressors. As compressed air is forced through the device's hollow-fiber membrane, oxygen and water vapor are discarded, while nitrogen remains at levels approaching 95 percent.

Although the commercial generators range from $4,000 to $20,000, the nitrogen-fills themselves typically go for $5 to $10 per tire. Top-offs are usually free.

"Today, consumers are paying for nitrogen," said John Lucidi, Parker Hannifin's nitrogen inflation product sales manager. "But in the future some progressive manufacturer is going to ship cars from the factory with nitrogen in their tires."

Perhaps. But as Goodyear spokesman Jim Davis points out, they will still need to regularly check their tire pressure.

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