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December 30, 2012

News & Features

Lightweights: Three materials compete to reduce vehicle weight

New York Times News Service

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Its aluminum body makes the 2013 Range Rover much lighter than older models. (Land Rover)

Thanks to tough new federal fuel-efficiency rules, automakers must meet a fleet average of 54.5 mpg by 2025. More efficient engines and electric powertrains can't carry the whole load, so carmakers and the federal government are pouring resources into "lightweighting" cars to meet the Corporate Average Fuel Economy, or CAFE, standards.

The Energy Department says that reducing a car's weight by 10 percent can improve fuel economy by 6 to 8 percent. Three technologies that show promise in lightening vehicles are high-strength steel, aluminum and carbon-fiber composites.

Drivers worried about running into older, heavier sport utility vehicles on the road might be reassured that these new materials are exceptionally stiff and strong, and will have to pass muster, including crash tests, with the National Highway Traffic Safety Administration.
Alan Hall, a technology spokesman for Ford, says it's too early to tell which of the materials will become dominant.

Steel

Not surprisingly, the steel industry is looking to retain its pre-eminent position in the business.

Ronald P. Krupitzer, vice president of automotive applications at a division of the American Iron and Steel Institute, says that about 60 percent of the average car by weight "is steel in one form or another." Since 2000, the industry has doubled the available grades of steel and increased strength levels by 50 to 100 percent.

"The steel available for car companies now is up to five times stronger than the steel used 10 years ago," he says. "A part that weighed 100 pounds is being replaced by one that's 75 pounds, with no price increase."

Krupitzer says steel doesn't yet offer the same weight savings as aluminum, another material in longtime use, but he says it's close and significantly cheaper.

Aluminum

While aluminum has been used for a century to build lightweight cars, Randall Scheps, director of ground transportation at Alcoa, says that it costs $600 to $800 more using aluminum to produce what automakers call "a body in white" — the car's basic structure before moving parts like doors and engines are installed.

Scheps offers a long list of advantages for aluminum. "It performs as well as steel in accidents, and it absorbs twice the crash energy per pound of mild steel," or older steel, he says. "An aluminum crash rail folds up like an accordion, which is exactly what you want it to do."

He points out the 2013 Range Rover, whose all-aluminum body is up to 39 percent lighter than older models. Scheps says the higher cost of aluminum is offset by lighter cars that require smaller engines, suspension and braking components.

Carbon fiber

That argument is also used in favor of carbon fiber, which is very light and strong but remains expensive. The BMW i3, a battery/electric car due in late 2013, will be the first mass-produced vehicle to use carbon fiber for the full body structure, which will sit on an aluminum chassis.

Greg Rucks, a transportation consultant, says that carbon fiber offers "unparalleled performance advantages," but estimates that replacing a steel body in white with carbon fiber would cost $1,200 per unit. Another hurdle for carbon fiber is a slower production process.

Despite all that, Rucks sees a business case for using carbon fiber today, because it offers lower tooling costs and manufacturing processes, as well as significant fuel savings for the customer.

It's safe to say that carmakers will increase their use of advanced steel, aluminum and carbon fiber. All offer big weight savings, and that's critical in the countdown to 54.5 mpg in 2025.

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