Tweel

tweel

The Tweel (a portmanteau of tire and wheel) is an experimental tire design developed by the French tire company 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 pneumatic properties.

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.

Eventually, it may be able to outperform conventional tires since it can be designed to have high lateral strength (for better handling) without a loss in comfort since the design of the spokes allows the vertical and lateral stiffness to be tuned independently. The tread patterns may incorporate holes in the design, significantly reducing aquaplaning. Because only the tread around the circumference would be disposed of when worn as opposed to a whole tire, the environmental impact should be less.

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. Also, long-distance driving at high speeds generates a great deal of heat, which leads to premature failure. The Tweel can also withstand a police ‘stinger’ spike strip.

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 skid steer loaders, 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 the Tweel remains mobile even with some of the spokes damaged or missing.

NASA has contracted Michelin to develop a wheel for the next generation Lunar Rover based on the Tweel. This has resulted in the Lunar Rover Initiative AB Scarab wheels.

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