Chemistry cuts tire’s rolling resistance

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Goodyear Assurance Fuel Max tires added a full mile to the 40-mi electric-only range of the 2011 Chevrolet Volt production car.

A new compounding additive that cuts rolling resistance is the key to Goodyear’s Fuel Max tire, the company’s recent upgrade of its midprice Assurance line, said Mark Cherveny, Passenger Tire Brand Manager in Akron, OH. The compounding agent means a car needs less fuel to keep a set of Fuel Max tires rolling, which can boost fuel economy by 4%. Lower frictional losses can add a mile per gallon of fuel to a 25-mpg car, which could save a couple of hundred dollars over the life of a set.

About a year and a half ago, Goodyear engineers came up with a way to cut the frictional heat that a tire typically generates as it rolls through the flat footprint on the pavement, Cherveny explained. Into the Fuel Max’s compounding mix went polymers (long molecular chains) that researchers had “functionalized” by attaching selected chemical groups. The chemical modifications allow the chains to take better advantage of another common compounding agent—silica filler, said the 30-year Goodyear veteran.

For the past few years, many tire makers have added silica (silicon oxide)—the principal component of sand and glass—to tire compounds to reduce rolling resistance and improve wet traction. The functionalized polymers alter the tread rubber so that it produces less heat as it undergoes constant flexing, stretching, and recovering during mechanical cycling. The special supplement, Cherveny said, enables “the silica to disperse better and incorporate into the polymer chains more completely” so less frictional heat results when the rubber distorts.

The additive turned out to be a rather simple and cost-effective upgrade of the existing Assurance all-season radial passenger tire, in some sense enabling Goodyear to bring low-rolling-resistance technology to the masses as many low-rolling-resistance tires are premium-priced or provide less tread life.

“We just added a different compound to the same mold,” he said, noting that the all-season tread provides wet/dry driving performance that equals or betters the competition. The tread life of Assurance Fuel Max tires is warranted for 65,000 mi (105,000 km), and the tires fit 80% of the passenger-car segment (about 38 million units), including most hybrid models. They are, for example, the exclusive fitment for General Motors' 2011 Chevrolet Volt extended-range hybrid. Fuel Max tires contributed 1 mi (1.6 km) to the car’s 40-mi (64-km) electric-only range.

In standard industry tests, Cherveny reported, the new Fuel Max tire exhibited 27% less rolling resistance—the force required to maintain forward movement—than the same-size regular Assurance tire. (The original Assurance model lineup was launched in 2008.) In track tests with the same cars at the Goodyear Proving Grounds, the new tire improved highway fuel economy by 4%.

“That result is in line with ‘industry-accepted knowledge’ that for each 10% you reduce rolling resistance, you gain around 1% in fuel economy,” he said. Efficiency gains for stop-and-go driving are smaller.

According to company estimates, the improved compounding saves 2600 mi (4200 km) worth of fuel over the life of the tire. Cherveny placed the effect on fuel economy in context by observing that “maintaining air pressure regularly is still more important for improving gas mileage.”

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