DUNEDIN — With the promise of nearly $150,000 in energy-efficiency stimulus funds, city staff agreed that an 80-gallon nitrogen generator would be a smart buy.
The generator, they wrote in their federal grant application, would replace the air pump at the city's public works facility, where Dunedin's nearly 300 cars, trucks and heavy-duty vehicles are serviced.
Filling tires with nitrogen, they said, would save 6 percent in fuel, extend tire life by 25 percent and "promote energy efficiency through public demonstration." The city budgeted $21,000 for the project.
Those savings would be huge — if they were true.
But experts say results like that are unrealistic. The benefits — slight, if any — of inflating with pure nitrogen are outweighed by the generator's high price, a cost made unnecessary by the cheap and easy alternative of monthly air checks.
"I can't see any reason why there would be a useful difference between nitrogen and air inside the tire," said John Heywood, director of MIT's Sloan Automotive Laboratory. "I'm not saying there's zero difference. I'm just saying it's not going to show up."
Nitrogen's strong point is the size of its molecules — they're larger than oxygen's and leak from tires slower, according to the National Highway Traffic Safety Administration. Supporters say nitrogen keeps tires inflated longer, meaning lower friction with the roadway, less fuel usage and less worn treads.
But even supporters, like the Get Nitrogen Institute, an organization sponsored in part by corporations selling nitrogen generators, say vehicles with well-maintained, air-filled tires would get a 2 percent boost in fuel from a switch to nitrogen — a third of the city's claim.
Institute representative Chris Lein estimated passenger vehicles could get about a 30 percent extension in tire life with nitrogen, and that the gas would also prevent oxidation and water vapor from deteriorating rubber over time.
But that estimate reflects the impact of constantly driving with under-inflated tires. With proper tire changes and monthly maintenance, air, which is 78 percent nitrogen anyway, can work just as well at a small fraction of the price, said Dan Zielinski, spokesman for the Rubber Manufacturers Association, which represents companies like Goodyear, Michelin and Bridgestone.
"The type of inflation gas you may use in your tires is not the question. The question is, do you properly inflate your tires," Zielinski said. "Compressed air works fine. You want to use nitrogen? That works fine, too. Just don't think that nitrogen relieves you of any pressure for regular tire maintenance."
Compressed air "has been used for the last century to inflate tires, and it has been a very safe practice," Zielinkski said.
Tires checked regularly for pressure, regardless of the gas, will provide identical mileage and tire life without the need of novel expenses.
"There are new ideas and inventions in the automotive area where some advocate says, 'this is fantastic, this will do this,' " Heywood said. "Only a few of these are well-founded."
Drew Harwell can be reached at firstname.lastname@example.org or (727) 445-4170.