When Tim Rhyne sat down with fellow Michelin engineer Steve Cron over lunch in the late 1990s, they didn't set out to reinvent the wheel. Tasked with defining the qualities of a pneumatic tire, the engineers sketched out a radial tire that didn't require any air. The result was the Tweel—a mash-up of "tire" and "wheel"—which mimics the performance of a radial tire using a circular shear beam and flexible spokes.
"It was a eureka moment over lunch," says Rhyne, now a senior research fellow with Michelin Tweel Technologies (MTT). Unlike a solid wheel with rigid spokes, the Tweel maintains ground contact pressure like an air-filled tire. "The beam deforms almost entirely in shear, no bending," says Rhyne. "It maintains contact pressure, and the spokes determine stiffness."