by Jim Kerr
The auto show season is in high gear and the auto manufacturers are displaying the latest production and concept vehicles. The concepts garner much of the attention because of their innovative styling and the potential for them to become future production vehicles. What many people don’t notice are the tires that roll under these concepts. The tires sometimes have as big a story to tell as the vehicles they support.
Some of the tires seen on concept vehicles are custom built, hand cut, one-off designs. Built using fairly standard technology, the tires have tread patterns cut into the rubber with a design that complements the concept vehicle. I have seen treads with footprints on them to imply sure-footed handling, V8 emblems in the tread to imply power and round knobs for tread to portray excellent off-road capabilities. These tires are also large – 20, 22, and even 24 inch tires are used because big tires fill wheel wells and make the vehicles stand out.
While some tires are just for show, others may be the tires of the future. This year at the Detroit auto show, Michelin showcased three new technologies. They named them the “Tweel”, the “Airless” and the “Michelin Active Wheel”. Each of these is more than just a tire. They are tire and wheel combined. Hence the name for the first concept, the Tweel.
The Tweel replaces the conventional air-filled tire and wheel with a band of composite reinforced tread wrapped around a flexible deformable wheel. The deformable part of the wheel looks deceptively simple. A honeycomb style centre supports composite polyurethane spokes that hold the tread. The spokes and hub can flex to absorb road shock and impacts yet can return to their original shape instantly to provide traction again. The flexible design acts like an air filled tire with similar ride and comfort, but with some not so obvious advantages.
The Michelin Tweel equipped Segway Centaur (left) and IBOT unveiled at the North American International Auto Show. Photo: Rick Dole. Click image to enlarge
Conventional tires are a compromise between soft ride and crisp handling. Stiffen the sidewalls and the handling improves but ride suffers. Soften the sidewalls and the ride may be fine but handling is spongy. Not so with the Tweel. Michelin is able to tune the Tweel so that the vertical stiffness and lateral stability are independent of each other. Both ride comfort and lateral stiffness can be optimised so drivers will get the best combination of ride comfort and superior handling not possible with conventional tires.
Other advantages of the Tweel are a tread that can be replaced without replacing the hub and spokes and of course, there is no air in this design so there is no checking air pressures, tire pressure monitoring devices and best of all, no flat tires.
The Michelin Tweel is demonstrated on a Caterpillar skid-steer loader. Photo: Rick Dole. Click image to enlarge
At the Detroit show, Michelin showcased the Tweel on the Audi A4. While the Tweel is still a concept tire for passenger cars, this remarkable tire/wheel combination is already in production for small mobile equipment such as the iBOT stair climbing mobility device and the Segway four wheel Centaur, another personal mobility vehicle. Michelin intends to enter the market with low speed, low weight applications for the Tweel but has additional projects planned for larger vehicles such as construction skidsteers and military vehicles.
The Airless, another Michelin concept, appears to be several pieces of solid rubber stacked in a circle around a central ring and capped with a band of tread. Again this tire holds no air and can’t become flat. The rubber’s elastic qualities enable the tire to support a vehicle yet absorb impacts and provide stable handling. The Michelin Airless is currently being tested on cars and motorcycles but could meet a large range of applications.
Finally, the Michelin Active Wheel uses a conventional tire but replaces the wheel with a module that incorporates the vehicle’s suspension, brakes and propulsion. An electric motor in each wheel moves the vehicle, eliminating the vehicle’s transmission, differentials or drive axles. The motor can also act as a generator to assist the brakes in slowing the vehicle. Springs and damping units are built right into the assembly to support the vehicle’s weight and allow the tire/wheel assembly to move up and down.
These three concepts may sound far-fetched, but so did the radial tire when Michelin introduced the concept over 55 years ago. These concepts are possible. Perhaps you will drive on them sooner than you think.