Those Wheels Keep On Turning Bart Thompson laughed as he compared the visual appeal of Michelin's latest innovation to the woman in a red dress from the first Matrix movie. As the engineer who is leading the development of Michelin's radical, pinwheel-style tire concept, it's no surprise that this project would excite his imagination. Still, he was making a point: The Tweel looks like no tire you have seen before. The look of wheels and tires rolling down the road or tucked into a body that's been dropped is one of the defining qualities of a custom truck and is stamped into the brains of most enthusiasts. But, one glance at the Tweel and all your expectations of how rolling mass should look get tangled in the Tweel's polyurethane spokes. There's more to Michelin's invention than a bit of automotive T&A. As you can see from the pictures, the spokes and tread belt are designed to flex. Fortunately, the spokes have excellent flex fatigue in that they snap back after bending, and have good creep resistance so that the Tweel maintains its round after sitting stationary for a long time. Compare that to a shelf that acquires a permanent sag from the heavy weight of the books resting on it-an example of poor creep resistance. The tread is reinforced with a proprietary composite to help maintain its stiffness. That combination of flexibility and stiffness is what makes the whole thing work.
How does the Tweel perform? Michelin's Audi fitted with a prototype Tweel "handles like it's on rails," according to Thompson. He says that the tread pattern and rubber of the Tweel give it adhesion characteristics similar to a regular tire and wheel.
Also, a regular tire is connected to a wheel in two places, the left and right edges, but the Tweel makes contact all across the width of the wheel, and the spokes run across the full range of the structure, giving it great stiffness. The Tweel is five times stiffer, laterally, and just as stiff, vertically, as a regular tire. And the combined weight of the Tweel's "tire and wheel" is about the same as a traditional combo. As for fuel efficiency, the Audi version has about the same efficiency as the Audi's stock, high-performance tire. "The pneumatic tire is very good for low roll resistance," said Thompson. "It's going to be hard to beat, but I think we can approach it." Thompson mentioned that you can drill holes into the Tweel, and it still will work. Hinting at a possible military application, he said that it can roll over a land mine and still do its job. And the wear life of the Tweel is 2-1/2 times better than a regular tire.
Since its soft debut in the Paris Motor Show late last year, the Tweel has attracted significant attention from the automotive industry, the Department of Defense, and even NASA. But, when will you see it hit the open market? The Tweel will appear on Segway's quirky personal transporters and on the Caterpillar Bobcat. As for automobiles, that Audi testbed will be it for a little while. Thompson wants to learn more from these low-speed applications and to otherwise refine the product before releasing it for the higher-performance automotive world. For example, one problem that needs to be worked out is the noisy vibration made by the spokes when the Tweel spins at high speeds. That's nothing like the noise Michelin's likely to hear if it manages to create a Tweel we can put on cars, trucks, and SUVs.
Putting Our Backs Into It We're revealing a little more backbone this issue, as we slowly but surely unveil the full splendor of our studio-shot beauty. For more information on AIM (our spinal image sponsor), point your browser to www.truckin.com.