One thing unites all cars built for the road, from the dumpiest Chevy sedans to the most erotic exotics. In the eyes of a wind tunnel, they are all pigs.

“What about the almighty sleekness of a Lamborghini or a Ferrari?” you might ask. To the wind tunnel they look like Conestoga wagons, or Spanish galleons, or equestrian statuary. We are talking air resistance here, or drag, caused both by automobiles’ size and irregular shape. Rub your eyes and look again. Bumpers, mirrors, wheels and tires, windshields the size of dining...