Reinventing the wheel – the airless tire

One of the more fascinating developments in the history of the automotive tire is the modern concept of the airless tire. Dunlop produced the first pneumatic tire for bicycles in 1888 and Michelin did likewise for cars in 1895, and for the last century, pneumatic tires have ruled. Michelin announced its airless Tweel technology three years ago (Gizmag’s biggest story ever with more than a million page views) and won the Intermat Gold Medal for Innovation in 2006, though we have yet to see a commercially available automotive product from the French giant. Now a new airless tire using a flexible, honeycomb-like internal structure could again prove to be a disruptive technology in one of the world’s largest industries. With development funded by the U.S. DoD, the initial aim of the project was to replace the Achilles heel of the military vehicle, but now the technology looks like going commercial for the rest of us.

Wisconsin-based start-up Resilient Technologies LLC is working on a four-year, US$18 million project with the U.S. DoD (Department of Defense) and the University of Wisconsin-Madison to research and develop a non-pneumatic tire for use on heavy-grade military vehicles such as Humvees. Tires have proven to be the weak link in Humvees, which can be immobilised by the scourge of the 21st century urban battlefield, the IED (Improvised Explosive Device). Once the mobility of a Humvee is compromised in a hostile environment, its inhabitants’ life expectancy closely approximates zero. As neither Michelin’s Tweel nor Resilient’s Airless tire do not have a tire-like pressurized air cavity, they cannot be punctured, thus assuring continuous mobility.

"You see reports all the time of troops who were injured by an IED or their convoys got stranded because their tires were shot out," says Mike Veihl, general manager of Resilient. "There's all sorts of armor on the vehicle, but if you're running in the theater and get your tire shot out, what have you got? You've got a bunch of armor in the middle of a field."

The company has made remarkable strides in just over two years of operations, cycling through literally hundreds of prototypes, developing subscale airless tires for lawn tractors, and finally the featured product: In April, Resilient installed a set of its creations on a Wausau-based National Guard Humvee, where it is undergoing rigorous on- and off-road tests.

Company reps say that Resilient's partnership with UW-Madison's Polymer Engineering Center (PEC) has played a major role in setting the high-speed development pace. The center serves as a subcontractor in the project and provides two graduate students under the general direction of mechanical engineering professor Tim Osswald.

In addition to conducting basic polymer research, the PEC works with dozens of companies, big and small, on materials testing and product development, says Osswald. The Resilient project presented one of the more complicated challenges his lab has seen, given the complete rethinking taking place in the design and the high levels of performance the tire must meet.

The Wisconsin design breakthrough, first developed by Resilient's in-house design and development team, takes a page from nature. "The goal was to reduce the variation in the stiffness of the tire, to make it transmit loads uniformly and become more homogenous," Osswald says. "And the best design, as nature gives it to us, is really the honeycomb."

Osswald and graduate students Nick Newman and Eric Foltz ran tests and simulations that helped Resilient confirm the quality of its unique design concept. They also studied other airless tire designs, including Michelin's "Tweel," to determine their properties compared to the Resilient design.

The patent-pending Resilient design relies on a precise pattern of six-sided cells that are arranged, like a honeycomb, in a way that best mimics the "ride feel" of pneumatic tires. The honeycomb geometry also does a great job of reducing noise levels and reducing heat generated during usage - two common problems with past applications.

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