The Tweel (a portmanteau of tire and wheel) is an experimental tire design being developed at Michelin. The tire uses no air and therefore cannot burst or become flat. Instead, the Tweel's hub connects to flexible polyurethane spokes which are used to support an outer rim and assume the shock-absorbing role of a traditional tire's sidewall.
The Tweel consists of a cable-reinforced band of conventional "tire" rubber with molded tread, a shear band just below the tread that creates a compliant contact patch, and a series of energy-absorbing polyurethane spokes. The rectangular spokes can be designed to have a range of stiffnesses, so engineers can control how the Tweel handles loads. The inner hub contains a matrix of deformable plastic structures that flex under load and return to their original shape. By varying the thickness and size of the spokes, Michelin can generate a wide array of ride and handling qualities. The tread can be as specialized as any of today's tires and is replaceable when worn.
The Tweel prototype, demonstrated on an Audi A4, is within five percent of both the rolling resistance and mass levels of current pneumatic tires which means the fuel economy should be within one percent of the OE fitment. Additionally, the test tire on the demonstration Audi has lateral stiffness five times that of the OE tire, providing exceptionally responsive handling.
The Tweel does have several flaws, however, the worst being vibration. Above 50 mph, the Tweel vibrates considerably. That in itself is a big problem, but it also causes two other things: noise and heat. A fast moving Tweel is unpleasantly loud [Source: CBS News]. Also, long-distance driving at high speeds generates more heat than Michelin engineers would like, which might lead to premature failure.
Given the high speed problems with the Tweel, the first commercial applications will be in lower-speed, lower-weight vehicles such as wheelchairs, scooters, and other such devices. The iBOT mobility device and Segway’s Concept Centaur were both introduced with Tweels. Michelin also has additional projects for Tweel on small construction equipment, such as skidsteers, for which it seems well-suited.
The first large-scale applications may be in the military where a flat-proof tire would be advantageous. Military testing has indicated that the Tweel deflects mine blasts away from the vehicle better than standard tires, and that Tweel remains mobile even with some of the spokes damaged or missing.