Reinventing the Wheel: a Guide to Michelin’s Airless Tire

Ever since John Boyd Dunlop patented the pneumatic tire, in 1888, the evolution of this vital item for the auto industry and for many other industries has seen many improvements, but none such revolutionary as Dunlop’s. That's until 2005, when industry leader Michelin presented the Tweel to the world. The name is a combination between the words “tire” and “wheel” and stands for a revolutionary concept: the airless tire. How it works
Michelin TweelMichelin TweelMichelin TweelMichelin Tweel
The Tweel doesn’t use a traditional wheel hub assembly. A solid inner hub mounts to the axle and is surrounded by polyurethane spokes arrayed in a pattern of wedges. A shear band is stretched across the spokes, forming the outer edge of the tire. On it sits the tread, the part that comes in contact with the surface of the road.

The cushion formed by the air trapped inside a conventional tire is replaced by the strength of the spokes, which receive the tension of the shear band. Placed on the shear band is the tread, the part that makes contact with the surface of the road. How does it work? When the Tweel is running on the road, the spokes absorb road defects the same way air pressure does in the case of pneumatic tires. The flexible tread and shear bands deform temporarily as the spokes bend, then quickly go back to the initial shape. Different spoke tensions can be used, as required by the handling characteristics and lateral stiffness can also vary. However, once produced, the Tweel’s spoke tensions and lateral stiffness cannot be adjusted.

When testing the new tire on an Audi A4, Michelin used Tweels made with five times as much lateral stiffness as a conventional tire, resulting in “very responsive handling” (according to the company). Journalists who tested the Audi A4 rolling on Tweel prototype tires confirmed the car was unusually responsive in its handling compared to a car on conventional tires. However, Michelin said that the Tweel prototype tire’s rolling resistance and mass are five percent higher than in the case of a pneumatic tire. The fuel consumption is also increased, by 1 percent, but since the Tweel is in an early stage of development, the numbers are expected to improve. Taking these drawbacks into account, why does Michelin continue to invest in developing the Tweel?


Well, one of the greatest advantages of this technology would be the fact that the tire is service-free. No more air pressure check, no more flat tires and no more blow-outs mean a lot less to worry about when driving your car. It is also conceived to last longer. Also, the balancing between traction and comfort could become a thing of the past. That’s because Michelin has found that it can tune Tweel performances independently of each other, which is a significant change from conventional tires. This means that vertical stiffness (which primarily affects ride comfort) and lateral stiffness (which affects handling and cornering) can both be optimised, pushing the performance envelope in these applications and enabling new performances not possible for current inflated tires.

Because it doesn’t require maintenance and it is risk-free, the Tweel tire could be a good choice for special vehicles like those used in the army, in the construction business or even in the exploration of other planets. And no, we’re not kidding on the last part. In 2009, Michelin has developed for NASA a Tweel-based tire to be used in the latest generation of lunar rover vehicles. The Michelin Lunar Wheel maintains flexibility and constant ground pressure, allowing the vehicle to move through loose soil and craters. In addition, it combines low mass and high payload capacity, making it 3.3 times more efficient than the original Apollo Lunar Rover wheels. Its textile tread enables the rover to maintain traction at very low temperatures.

Tweel technology could also penetrate the personal mobility market. At the public demonstration of the Tweel, Michelin placed prototypes on the iBOT, a personal mobility device for physically impaired people, and the Segway Centaur, a four-wheeled ATV-type vehicle that uses Segway’s self-balancing technology.


But even if the Tweel could have many applications, it is not the perfect tire. At least not yet. One of its biggest flaws is vibration. Above 50 mph, the Tweel vibrates considerably, thus generating noise and heat. A fast moving Tweel is reportedly unpleasantly loud. Long distance driving at high speeds generates more heat than Michelin engineers would like. That’s why, for the moment, the first applications of the Tweel are in low-speed vehicles, such as construction vehicles. The Tweel is perfect for such use because the ruggedness of the airless design will be a major advantage on a construction site. Michelin is also exploring military use of the Tweel, which would be ideal in combat situations, where conventional tires are an easy target.

Another big obstacle in the Tweel’s way is the tire industry itself. Making Tweels is quite a different process than making a pneumatic tire. The retooling of the many tire factories, plus the equipment necessary to service the new tire around the world represents also an important obstacle to the broad adoption of airless tires. Because of these drawbacks, Michelin is not planning to roll out the Tweel to consumers any time soon. “Radial tire technology will continue as the standard for a long time to come,” read Michelin’s press release.

Last but not least, another challenge for the Tweel could be the drivers themselves who would see their beloved radial tires and rims replaced by a not so good looking Tweel. Of course, Michelin could place some covers to hide the spokes, but the psychological impact on the consumer should not be neglected. Oh, and Michelin should not rest on its laurels. It might be the inventor of the Tweel, but another company is working on a similar project. Resilient Technologies is developing their own airless tire, known as the NPT (non-pneumatic tire). That company is using a more aggressive development and marketing strategy aimed at military use. The NPT is based on a different configuration of spokes, but the general idea is the same as Tweel's.
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