The spin on tires and fuel economy
William Lowry recently spent $500 to replace the tires on his Toyota Camry hybrid. The salesman said the Goodyear Regatta 2 tires were just as good as the Bridgestone Turanzas that came with the car. But it didn’t take long for Lowry to notice that his fuel economy had fallen by five miles a gallon.
“I would have paid more for tires that get better mileage. Instead, I spent extra money for the privilege of spending more money on gas,” said Lowry, a UCLA professor, who asked the tire dealer about fuel efficiency and was told all tires were the same.
In fact, when it comes to fuel consumption, not all tires are created equal. According to experts, efficiency can vary by as much as half from tire to tire, and can reduce fuel economy by 10% or more.
Yet consumers are in the dark about tire efficiency. With no standardized rating available, consumers often unwittingly choose tires that hurt fuel economy. Others who upgrade to oversize rims and low-profile tires -- which are known to increase fuel consumption -- may not realize what a price they’re paying.
Both California and the federal government have passed laws to label tires by fuel efficiency, but little progress has been made in implementing them. And even as the $34-billion tire industry spends huge sums trying to improve the efficiency of its products, tire makers oppose setting minimum standards that could save billions of gallons of gas.
Adding to the confusion are automakers, which in the face of the tough new fuel economy mandates of 31.6 miles per gallon by 2015 are pushing tire makers to produce more efficient tires yet at the same time are enlarging the size of wheels and tires on their vehicles for reasons of style.
“It’s very confusing,” said Susan Brown, senior policy advisor at the California Energy Commission, which is slowly implementing a 2003 law that would require tire efficiency labeling and establish an average efficiency standard for aftermarket tires. “With gas the price it is now, you’d think consumers would love to get more-efficient tires.”
As tires roll, their shape constantly changes, and energy that could be used to power the car is lost as heat. Factors such as tread pattern, composition, weight, width and height contribute to that energy loss, known as rolling resistance. All told, about 20% of fuel is used to overcome rolling resistance, according to Dean Weeks, technical marketing manager at Michelin, which has marketed low-rolling-resistance tires for 15 years.
Tire efficiency took a leap forward with the advent of radial tires, and since then the use of new compounds and tread patterns has helped even more.
According to Dave Cowger, General Motors Corp.’s top tire and wheel engineer, modern tires have on average about 50% less rolling resistance than those on the road in 1975, and “we are optimistic there can be more improvements.”
Tire makers supported the 2003 California law calling for a fuel-economy labeling system. They backed a similar provision in the federal energy bill passed in December that would create a national labeling system -- akin to the Energy Star system for rating household appliances.
But they opposed a provision of the California law that would set an efficiency requirement for tires sold in the state, and, the energy commission said, have dragged their feet on supplying data needed to implement both parts of the law.
The Rubber Manufacturers Assn., which represents tire makers, denies stonewalling. “We’ve been trying to be as cooperative as we can with this,” said spokesman Daniel Zielinski.
Such labeling is unlikely to roll out before 2010. In the meantime, there’s generally no way that consumers can discern what a tire’s fuel efficiency is; even dealers often don’t know.
A different California agency, the Air Resources Board, is considering measures to ensure that tires maintain proper air pressure, which can dramatically affect fuel economy. One possible step is a permeability standard that would require manufacturers to make more-airtight tires, a rule tire makers oppose.
Another issue is size. The trend toward bigger tires has been dramatic in recent years. According to Kelley Blue Book, the most popular factory wheel diameter for cars in 2000 was 15 inches. Today it’s 17 inches, with 45 models coming standard with 19-inch wheels this year (up from zero models in 2000). Michelin says its most popular aftermarket tire last year was 20 millimeters wider than in 2001.
That matters, because, all else being equal, bigger rims and wider tires are heavier, are less aerodynamic and create more rolling resistance. Yet consumers demand them, said Jamie Nichols, general manager of All Star Tire in Long Beach.
“A guy who wants big wheels will ask what the impact is on his mileage,” Nichols said. “But in the end what matters is cosmetics.”
Tire makers expect as much as a 50% reduction in rolling resistance in the next two decades. But such moves, Zielinski said, come with trade-offs in other important tire features, including traction, stopping ability and tread life. “There’s just no easy answer here,” he said.
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