WASHINGTON – To meet the strict new corporate average fuel economy rules under consideration by U.S. regulators for the 2016-2025 timeframe, future vehicles will have to be much lighter than their predecessors, experts say.

“It will take more than weight reduction, but it’s still very important to the overall picture,” says Doug Richman, vice president-engineering at Kaiser Aluminum.

Auto makers are eying a number of approaches to hitting historic CAFE hikes in order to move from today’s 27.3 mpg (8.6 L/100 km) to 35.5 mpg (6.6 L/100 km) by 2016 and potentially 62 mpg (3.9 L/100 km) by 2025.

These include electrification, downsized engines with turbo boost, diesel engines and more-efficient transmissions.

But to achieve 62 mpg, a vehicle also must shave an estimated 19%, or 712 lbs. (310 kg), off its current weight, Richman estimates.

“Whatever the pathway, weight reduction is necessary,” he says during a presentation at the recent Society of Automotive Engineers’ annual Government/Industry meeting here.

Many parts on today’s vehicles already leverage the lightweight benefits of aluminum.

According to Richman, 65% of all engine blocks have migrated from cast iron to aluminum, while 50% of the wheels on today’s cars and trucks have shifted from steel to aluminum. And nearly 100% of today’s cylinder heads are aluminum.

“They’re saturated,” says Richman, a former General Motors engineer whose new company already is capturing new product programs driven by vehicle light-weighting to meet pending CAFE standards.

The real growth for aluminum, he says, lies in closure structures such as doors and hoods. But Richman’s nirvana is the body-in-white.

A recent study commissioned by the aluminum industry and conducted by Aachen University estimates aluminum use at BIW could rise to 40%, translating into a weight reduction of 53% on a future vehicle, compared with today’s models.

The study also shows using aluminum in key components can safely reduce overall vehicle weight by as much as 40%, compared with 11% for high-strength steel.

Greater use, it suggests, could trim a vehicle’s overall weight as much as 525 lbs. (229 kg), for a fuel economy boost of 10%, or 2.7 mpg (1.1 L/100 km), from today’s cars and trucks.

This is not to say steel doesn’t have a role in the regulatory-intense auto industry of tomorrow. “At 62 mpg, there is room for steel in the auto industry,” says Ronald Krupitzer, vice president-auto market, at the Steel Market Development Institute.

“We have to keep reinventing steel,” he adds, noting in the coming years the steel industry will double its number of grades and further improve forming technologies.

For example, advanced and ultra-high-strength steel are two of the auto industry’s fastest-growing materials, the former Chrysler engineer tells a conference panel on meeting President Obama’s clean-vehicle challenge.

“Our goal is to get so close to the properties of aluminum, you won’t be willing pay for the difference,” Krupitzer says. He cites as an example the vehicle hood of one product program that steel lost to aluminum but gained back a year later with a better, cheaper alternative.

The industry’s onus to lose weight comes after years of bulking up. According to a recent Ward’s analysis, the average weight of a light vehicle grew from 2,896 lbs (1,261 kg). in the passenger-car dominated early 1990s to 4,018 lbs. (1,750 kg) by 2005.