More Traction For Fuel-Efficient Tires
The engineers who create gallon-squeezing cars like the Toyota Prius use every available method to comply with the ever-tightening fuel-economy standards they must meet. Those solutions may include the use of hybrid powertrains, adopting lightweight materials, cutting aerodynamic drag, and minimizing the friction losses of moving parts.
There’s another path to fuel efficiency that may be less attention-getting, yet rather effective: equipping the cars with low-rolling-resistance tires. Such tires can improve fuel economy by as much as a mile or two per gallon over conventional all-season designs — and more when compared with high-performance summer tires — according to automakers, making them an important tool of the pursuit of vehicle efficiency.
Given the high cost of developing engine technologies like turbocharging and direct fuel injection, working to improve tires can deliver worthwhile improvements for relatively small investments. The negative side of easy-rolling tires has been a lingering reputation, based on early examples, for compromised traction in wet conditions and, and in some cases, short tread life.
Tire companies say that advances in the materials used in the latest low-rolling-resistance tires, and in the manufacturing processes, have overcome the drawbacks.The good news for drivers is that tire manufacturers are starting to build the fuel-saving features into all tires.
On average, 5 to 15 percent of the fuel a car burns is used to overcome rolling resistance in the tires, according to the Energy Department. Rolling resistance is generated largely in the tire’s outer tread band, which deforms as it comes into contact with the pavement, then springs back.
The resistance caused by this flexing of the tread generates heat in the rubber, wasting energy without providing any benefit. The tire designer’s challenge is to let the tire flex enough for good contact with the road while minimizing internal friction and wear.
In the United States, the National Highway Traffic Safety Administration is developing updated tire labeling rules that will add grades for fuel efficiency to help consumers in selecting replacement tires. The new rules are expected to be adopted in mid-2013, said John Emerson, Director of Industry Standards and Government Regulations at Michelin North America.