Auto makers like low-rolling-resistance tires and the quick jump in fuel economy they can provide.
One car maker estimates that cutting 125 to 250 pounds from a light truck boosts its fuel efficiency by about 0.3 to 0.5 mpg. In contrast, switching to a tire with low rolling resistance can bring an increase of 1 to 2.5 mpg.
Such tires are standard on at least two 2010 vehicles. And in the automotive aftermarket, ads tout the tires' better fuel economy.
But have those tires' shortcomings been eliminated?
“You can get a tire that will give you better mileage, but you are going to give something up,” said Matt Edmonds, vice president of mail order and Internet marketer Tire Rack Inc. “Typically that would have meant stopping distance, handling in wet conditions.”
'Not quantum leaps'
In its independent tests, Tire Rack determined that “the manufacturers have spent a tremendous amount of time and effort in engineering to improve those areas, as well as improve the rolling resistance of the tire,” Mr. Edmonds told Automotive News, a sister publication of Tire Business. “But they are not quantum leaps by any stretch of the imagination.” Credit new tread compounds and tread designs for improvements.
For example, one tire showed an almost 5-percent increase in fuel economy in Tire Rack's testing. That same tire stopped the vehicle about 25 feet sooner than the baseline tire in a test of the distance required to stop the vehicle at 50 mph on wet pavement.
The Goodyear Assurance Fuel Max, a tire with low rolling resistance, is standard on the 2010 Ford Fusion S. The 2011 Chevrolet Volt will get the same tire. The 2010 Mercedes-Benz S400 hybrid uses Bridgestone's Potenza RE050 Ecopia. Both tire makers expect additional auto maker applications in the future.
Tire Rack conducted tests this past summer on the track at its headquarters in South Bend, Ind., using several 2009 Toyota Prius sedans.
It tested low-rolling-resistance tires from Bridgestone, Goodyear, Michelin and Yokohama. The baseline tire for the comparison was the Goodyear Integrity, which is the low-rolling-resistance tire that was standard on the 2009 Prius. Additionally, the Goodyear Assurance ComforTred tire was included in the test because it is a popular replacement tire for the Prius.
The test results showed that compared with the Goodyear Integrity, fuel economy increased nearly 5 percent with the Michelin Energy Saver A/S, which had the highest percentage increase in the group. Additionally, the Michelin tire stopped the Prius from 50 mph in wet conditions in about 107 feet, compared with nearly 132 feet for the Integrity tire.
Under dry conditions, the Integrity tire stopped the Prius in about 97 feet, compared with about 98 feet for the Michelin tire.
But Michelin's HydroEdge Green X—also marketed as a tire with low rolling resistance—tallied a roughly 1-percent decrease in fuel economy compared with the baseline Integrity tire.
The HydroEdge tire stopped in about 113 feet under wet conditions, about 19 feet less than the Integrity tire.
Why the difference between the two Michelin tires? The HydroEdge Green X tire has a tread pattern and compound engineered for a longer life, according to Doug Girvin, director of product marketing for passenger cars and light trucks at Michelin North America Inc. It comes with a 90,000-mile warranty. The Energy Saver A/S does not have a mileage warranty.
Mr. Edmonds said studies by the federal government show that a tire can raise or lower a vehicle's fuel economy by 4 to 7 percent.
Tires with low rolling resistance carry a price premium, Mr. Edmonds noted, but when the cost of the tire and the fuel cost savings were added up, it was a wash. A gasoline price of $2.50 a gallon was used for the computation.
“The tire that gives you the better mileage is typically a more expensive tire,” he said.
“When you take the cost of that tire and the cost of the fuel that it took over the life of that tire vs. a slightly less expensive tire that uses a little more fuel, the average cost-per-mile driven came within one-hundredth of a penny of each other.”
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