Automakers are putting their cars on a diet

With gas prices pushing past the $4-per-gallon mark, fuel economy has become a big issue for car buyers and carmakers alike. Yet many U.S. motorists still seem reluctant to embrace the sort of pint-sized vehicles that have become commonplace in markets like Europe and Japan.

“People don’t necessarily want to drive small cars,” stressed George Peterson, an automotive analyst with AutoPacific. “They want to drive bigger, more fuel-efficient cars.”

Given American car drivers’ tastes, some experts suggest that the challenge for automakers today isn’t to come up with a subcompact car that does 50 mile to the gallon. Instead, the challenge is to build a midsize model that can deliver 40 mpg.

Until recently, achieving that goal seemed like a fantasy, at least without using a costly hybrid drivetrain. But carmakers have come to discover a variety of other tools in their toolbox that can improve mileage substantially without downsizing, Peterson said.

At Ford, for example, they’re putting vehicles on a diet.

“In the mid-term, from now to 2017 or 2018, we’ll remove anywhere from 250 to 700 pounds, depending on the vehicle,” said Derrick Kuzak, Ford’s global product chief.

According to an industry rule of thumb, every 100 pounds added or subtracted from the mass of a vehicle has a one mpg impact on fuel economy, so Ford’s weight reduction strategy should yield anywhere from around two to seven miles a gallon in added fuel economy, everything else being equal.

Ford is by no means the only maker targeting heft. Hyundai pulled about 150 pounds off the curb weight of its new Accent subcompact, which helped it achieve a highway rating of more than 40 mpg.

And Honda is taking similar steps. John Mendel, chief executive of the automaker’s U.S. subsidiary, has said, referring to improving fuel economy, that “there are only so many levers you can pull, and two of the biggest are weight or size.”

As anyone who’s ever tried to shed a few pounds for a wedding or a reunion knows, dieting isn’t easy. And it’s especially tough for automotive engineers. Every year seems to bring new safety regulations demanding new equipment for cars, like stability control, or stiffer bodies that can survive the latest roof crush standards.

Add all the onboard features that consumers are demanding, from heated and cooled leather seats to twin headrest-mounted backseat video monitors, and the challenge of slimming down becomes even harder.

“Which is why, despite all our efforts in the industry to cut weight over the last decade, the weight of most vehicles have actually gone up,” lamented Carlos Tavares, president and CEO of Nissan Americas.

Worried about losing business, steel makers have been coming up with a variety of super-strong alloys that actually reduce the amount of metal needed in a car, even with the tougher roof crush standards.

But the industry is also migrating, where possible, to newer, lighter alternatives. The latest Jaguar XJ, for example, uses an aluminum body and chassis, while the new Porsche 911 GT3 RS 4.0 has super-light carpets.

The Porsche Cayenne redesign has shed a full 408 lbs with the use of lighter materials and a revised drivetrain. Across the line it gets at least a 10 percent mileage increase, yet with the twin turbo V8 model the car’s 0-60 acceleration time drops from 4.9 to 4.4 seconds.

Aluminum can shave hundreds of pounds off the weight of a conventional steel car body. And the metal is in steadily increasing demand, as is magnesium, which is used for such applications as the cross-beams mounted behind many modern instrument panels.

Plastic, in all its many forms, has become the material of choice for bumper fascias, interior trims and even some body panels — although the now-abandoned Saturn brand gave up on using the material for fenders and doors because of a nasty tendency to shrink and swell, depending on the outdoor temperature.

The material of the future, many are betting, is carbon fiber. Seemingly as light as air, the material has become extreme popular with manufacturers of high-priced sports cars, like Lamborghini, which uses carbon fiber for much of the new 200 mph Aventador sports car.

The problem is cost. Using carbon fiber in a car has traditionally required a price tag in the $200,000 range, but that may be changing. At the Geneva Motor Show earlier this year Mini showed off the Rocketman concept, which would use carbon fiber on a car priced at barely a fifth as much as Lamborghini’s Aventador. Mini’s parent, BMW, has invested in carbon fiber research, as have a number of other makers.

“Carbon fiber has potential if we can come up with ways to improve manufacturability and bring down costs,” said Ford’s Kuzak.

The Detroit automaker’s engineering czar stressed that it’s difficult to put an existing vehicle on a diet. Instead, it’s better to start with an all-new car platform. One of the advantages with this approach is that if you cut a few hundred pounds from a vehicle’s overall weight you can save even more by then adopting a smaller engine, downsizing the brakes and other components.

While Ford has been pushing to trim mass even faster than before, Nissan’s Tavares cautioned that “you should not only focus on weight reduction.”

There are plenty of other ways to impact fuel economy, including aerodynamics, improved tires and reduced-friction powertrains, he said. By investing in all these areas, automakers still have plenty of opportunities to improve mileage enough to let buyers downsize their fuel consumption without having to give up the larger cars they like.