Mustang versus Camaro. BMW versus Mercedes. Camry versus Accord. These are among the biggest rivalries in the automobile world.
Get ready for the next epic battle: aluminum versus steel.
"This has become a real competition," said Golam Newaz, an automotive materials engineer at Wayne State University in Detroit.
The growing contest between the two metals was evident in the new car introductions at the North American International Auto Show in Detroit this week.
Automakers are looking ahead to the stringent federal standard requiring a near-doubling of fuel economy by 2025. Putting cars on a diet is the only way to hit that goal.
When Ford Motor Co. introduced the next generation of its top-selling Ford F-150 truck this week, the completely re-engineered pickup featured aluminum from the hood to the tailgate. The new Ford truck is 700 pounds lighter than the one it replaces.
Here's why: A cubic centimeter of steel weighs about 8 grams, compared with just 2.7 grams for aluminum, Newaz said.
The F-series truck has historically been a drag on Ford's corporate average fuel economy, the statistic watched by regulators, said Mark Fields, the automaker's chief operating officer. Now, it will play a key role in boosting the average, Fields said.
Although Ford has yet to release fuel economy numbers for the truck, analysts at the show said it could reach up to 30 miles per gallon in highway driving.
Meanwhile, Mercedes-Benz debuted the next C-Class sports sedan, touting how its body will be built mostly with lightweight aluminum. The Benz weighs about 200 pounds less than the previous sedan.
Still, the switch to aluminum has its complications. Already there are reports of manufacturing delays as Ford goes mass market with a material previously reserved for car hoods or the bodies of small-volume luxury vehicles and sports cars.
Aluminum is more expensive to handle than steel and more complicated to stamp and weld, requiring higher heat and more electricity.
Another hitch is that it can add to the expense of repairs, and not as many body shops know how to work with it, said Larry Dominique, president of auto valuation company ALG Inc. and the former vice president of product planning for Nissan in North America.
That's less true than in previous years and will fade as more aluminum is used in popular models, said Kevin Lowery, a spokesman for Alcoa, the aluminum company.
When Audi introduced its A8 luxury sedan with an aluminum chassis two decades ago, "there were only a handful of shops capable to repair it. It had to be shipped to one of those centers to be fixed," he said.
But now the metal is the second most used material in making cars, and its utility is growing beyond car hoods, its most common application, Lowery said.
"The next frontier is in doors and the body," Lowery said.
Alcoa projects the use of rolled, sheet aluminum for auto production will grow tenfold by 2025.
The company is pouring money into factories to ramp up.
It just completed a $300-million expansion of a plant in Davenport, Iowa, exclusively for automotive production. And it is launching a $275-million expansion of a plant in Knoxville, Tenn., to be completed late next year.