GREENVILLE, S.C.--The first automobile to use air-filled tires was a racecar built by André and Édouard Michelin in the early 1890's. More than a century later, the French company founded by the Michelin brothers is so identified with pneumatic tires that its mascot, Bibendum, is a man made of little else. Now, after decades spent persuading the world to ride on air, the company has begun work on an innovation that could render the pneumatic tire obsolete. Engineers at Michelin's American technology center here envision a future in which vehicles would ride on what they call the Tweel, a combined...