Auto components lighten up to improve mileage

— -- Automakers are putting cars on a diet in a bid for better gas mileage.

They are finding ways to shave pounds from car bodies — from the hood to the back bumper — often by substituting plastic, composites and aluminum for steel.

When they use steel, it is often a higher-quality grade that delivers more strength and less weight.

Every 120-pound reduction can yield a 1% gain in gas mileage, says Bill Grabowski, director of body core engineering for Chrysler. Best of all, if engineers can make the body lighter, other components, such as brakes, suspension and the engine, can be lighter, too. And the vehicle won't need as much gas-guzzling horsepower to push it around.

Driving drastic weight-loss plans: the prospect of tougher government-mandated fuel-economy standards. Facing that possibility, "We will focus on almost nothing but ways to improve our fuel economy for the next five years," Grabowski says.

But it won't be easy. Even as engineers are trying to find ways to eliminate excess weight, government and consumers are demanding new features that add pounds. Some offer safety, such as side-impact protection and protection from roof crushing. Others are luxury touches such as glass roofs or rear-seat entertainment systems. A glass roof alone can add up to 200 pounds.

Ford replaced steel with aluminum in the brakes (7.5 pounds), redesigned the rear seat (10.7 pounds) and changed the carpeting in the trunk (3 pounds). Using aluminum wheels instead of steel saved 22 pounds on Focus.

Due to those and other changes, Focus will be up to 5% more fuel efficient than the old version.

Taking the heft out:

•Lighter materials. The Infiniti EX35, which goes on sale in December, has a plastic rear hatch and aluminum bumper supports, suspension components, hood and wheels. Infiniti parent Nissan says the goal was to make the luxury sedan weigh about 60 pounds less than comparable BMW and Lexus models.