Inventing the Tweel

Much of the technology that is used on modern cars, though it has been incrementally improved over the decades, is still built on the same basic concepts that were used on history’s first automobiles. Windshield wipers, for example, have not seen much improvement at all. Another aspect of modern automobilery which is little more than a polished up version of the original design is the classic wheel-and-tire combination.

In 1901, the Oldsmobile “Curved Dash Olds” became the world’s first high-volume mass-produced automobile, and it was a contraption which looked very different from cars today. It resembled a carriage more than it did a car; it was started with a seat-side crank, steered with a “tiller” lever, and when the four-horsepower engine started pinging, the driver simply used a hand-operated dispenser to feed the it more oil. But one thing it did have in common with modern cars is that it came with a set of metal rims wrapped with rubber tires. They were narrower and flimsier back then, but in principle, they’re not so different from what you’d find on an automobile today. Now, over one hundred years later, Michelin is developing what looks to be the next evolutionary step in tire/wheel technology. They call it the Tweel.

The word “Tweel” is a portmanteau of “tire” and “wheel.” Michelin’s prototypes integrate the tire and wheel into one component, and the use polyurethane spokes in place of the air in a traditional tire. This design completely eliminates the problem of flat tires and blowouts, and allows the tire to deform locally in a way which very effectively absorbs shock.

A tweel’s vertical stiffness (which primarily affects ride comfort) and lateral stiffness (which affects handling and cornering) can both be exactingly optimized for a particular application. A tweel’s design also seems to be more conducive to “capping,” where the tread of the tire is replaced rather than the entire unit. This would reduce tire maintenance costs for vehicle owners, and sharply reduce the amount of waste rubber generated by discarded automobile tires.

One aspect of tweels that seems conspicuously left out of the available information is its braking performance. The same property which allows the Tweel to absorb shock so effectively might also make it lousy during hard braking, causing the tire’s leading edge to flatten and deform in undesirable ways. The Tweel’s construction may also cause slightly more drag during normal driving, reducing fuel efficiency and tread life. Another overlooked data point is the shear strength of the polyurethane spokes in a tweel; it would be interesting to learn whether they can withstand hard steering at high speeds without tearing.

Tweels are already being produced for use in some lightweight applications such as the iBOT mobility system, a wheelchair-like device which can navigate stairs and uneven terrain. But tweels for heavier applications such as cars are still in the early prototype phase. Initial tests show excellent performance, but some vibration problems must be overcome to eliminate excessive noise. But once tweels are ready for heavier applications, the military may be Michelin’s first customer; flat-proof tires which effectively absorb bumps would be extremely advantageous to vehicles moving in difficult or dangerous areas.

Further info:
Press release from Michelin
CBS News segment on the Tweel (Windows Media)