The Airless Tire

A follow-up to the article “Reinventing the Wheel,” which discusses the direction that non-pneumatic tires could take in the future.

By Heather Ruhl Photos by Samuel Fritz Print Design by Lukas Lindquist
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Imagine a world where vehicle tires could not be popped, and if you ran over a pothole, you would not have to go through the dangerous process of changing a tire on the side of the road. This could all be possible due to an innovative non-pneumatic tire that was developed here on the UW-Madison campus.

The magazine first covered this story in the April 2009 article ‘Reinventing the Wheel.’ At the time, the U.S. Department of Defense hired the Wausau-based Resilient Technologies in collaboration with the UW-Madison Polymer Engineering Center (PEC) to develop a non-pneumatic (airless) tire to be used on heavy-duty military vehicles similar to the Humvee. The goal of the project was to design a tire that would be able to continue being driven on even after part of it had been blown off. This means that the vehicles’ tires could be neither shot off nor could they be blown off, at least not as easily as with traditional tires.

Resilient Technologies and the UW-Madison PEC spent the next two years in exhaustive design and testing to develop the current product: an injection molded non-pneumatic tire with a honeycomb-like support structure. This design is currently being utilized by the U.S. Military.

Similar to anti-lock brakes, which were initially developed for the military, this technology has recently become commercialized. The Polaris Sportsman WV850 H.O. ATV has recently hit the market, becoming the first commercial product to have these non-pneumatic tires. This product even made Popular Science’s “The 10 Best Things from February 2014” list. Both of the vehicles on which the non-pneumatic tires are being used are specifically off-road vehicles, not commercial vehicles.

It would be very low maintenance, and you could gear the bicycle tires to certain softness or hardness; you would have a lot more to play with than just pressurized air

Professor Osswald

This is because, despite their many advantages, non-pneumatic tires are still not widely utilized, which begs the question, “Why?” According to Osswald, there are still some design improvements that would need to happen in order to make commercial mass production viable. “There is one step still…which is building the sidewall,” Osswald states. He explains that this is an important and semi-difficult step towards making the tire a universally useful product. While the sidewall is not needed on the vehicles on which the tire is currently being used, it would be important to develop a design that included a sidewall before it could be used on regular vehicles.

As seen in the current design, the tire has no sidewalls, only the exposed honeycomb structure. Without the sidewalls, the tires would not operate well on a commercial scale. This is because the sidewalls prevent debris from getting stuck in the honeycomb support structure and unbalancing the tire itself. This would be an especially important feature in areas, such as Wisconsin, that get snow during the winter. Without the sidewalls, the snow and salt from the roads would get caught in the tire itself. However, designing a sidewall is not so simple. “[The tire] has to be closed, and if that’s the case, you are going to have a much harder time conducting the heat out from the inner structure,” Osswald predicts. This could lead to problems with the tire overheating and could potentially lead to cooling systems being placed in the non-pneumatic tires.

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To balance this design challenge, there are advantages to airless tires besides their inability to burst. These additional advantages to using non-pneumatic tires could include: better gas mileage, easier manufacturing and higher variation of materials that could be used to give different ride qualities.

Even though there are challenges to creating a fully marketable product, Osswald feels it is something he would like to see come to pass. He feels that the commercial market for non-pneumatic tires is heading towards specialized vehicles, like bicycles, ATVs, larger trucks and, possibly later on, regular cars. “It would be very low maintenance, and you could gear the bicycle tires to certain softness or hardness… you would have a lot more to play with than just pressurized air,” Osswald says. In specializing the material for each application, there could be different tires used for racing bikes and mountain bikes, optimizing the performance of both. It could also mean that sports cars and trucks could have different tire materials that could also enhance not only the ride quality based on the requirements of each vehicle, but also vehicle performance. Non-pneumatic tires allow for more options when it comes to performance, as there are more material options than merely “air.”

While non-pneumatic tires may not be in mass production today, it is possible that they may solve many of the problems with current standard issue vehicle tires. As presented in the “Reinventing the Wheel” article, the non-pneumatic tire has many real-world applications already, and all it would take is some additional development to make them ready for the standard market. In the future, this could lead to improved ride quality and better safety. Airless tires include the best of all worlds.