TOPSHAM, Maine — Many motorists seeking to improve their mileage as gasoline prices soar this summer are examining everything -- right down to the air in their tires. And for a growing number, plain old air isn't good enough.
George Bourque of Fairfield, Maine, is among those driving around on tires filled with pure nitrogen, the same stuff that NASCAR racers use.
Bourque, an engineer, said he had seen an improvement in fuel economy of 1 to 1.5 miles per gallon since he began filling his tires with nitrogen. Proponents say the gas maintains tire pressure longer and resists heat buildup on hot summer days.
"I analyze everything," he said.
Nitrogen has been used for years in the tires of race cars, large commercial trucks, aircraft and even the space shuttle. But it is finding its way into the mainstream at a growing number of tire dealers -- including Costco Wholesale Corp.
Nationwide, fewer than 10% of tire dealers offer nitrogen, but the number is growing, said Bob Ulrich, editor of Modern Tire Dealer magazine in Akron, Ohio. Most dealers charge $2 to $5 a tire for the initial nitrogen fill-up, he said; they generally offer free lifetime refills.
Bourque got his tires -- filled with nitrogen -- in Waterville, Maine, at Tire Warehouse Inc., which has 50 dealerships across New England. The nitrogen was part of the installation package when Bourque bought a new set.
Skeptics question how much can be gained by filling tires with pure nitrogen when the air we breathe is already 78% nitrogen.
The differences are subtle but important, said Steve McGrath, Tire Warehouse's vice president of marketing in Keene, N.H.
Nitrogen molecules are bigger than oxygen molecules, so nitrogen seeps out more slowly from tires than air; nitrogen resists heat buildup better than air, which contains moisture; and nitrogen reduces oxidation, which can damage the tire from the inside out, proponents say. Nitrogen is an inert gas, so there are no safety or environmental issues.
Those advantages are important in vehicles equipped with tire pressure monitoring systems, which are sensitive to changes in tire pressure, McGrath said.
With or without nitrogen, proper inflation is a key to improving fuel economy. Motorists can improve mileage by about 3% simply by keeping their tires properly inflated, the Energy Department advises.
