When Scotsman Robert Thomson invented the pneumatic tire a century and a half ago, a rubber doughnut inflated with air was only one of several ideas he proposed. It seemed like a good idea but he was concerned about how one would keep the air contained within this new type of tire. Other designs he had involved filling his proposed tire with sponges, springs and even horsehair. The object of all of this, of course, was to have a tire that absorbed shocks and thus provided a comfortable ride regardless of what the road conditions are. Even though the pneumatic tire had yet to be perfected, research was being put into tires that weren’t inflated by air.
Airless tires on the Moon
Despite over 100 years of success with pneumatic tires, the concept of an airless tire appeared once again, but this time on the Moon. Yup, in the 1970s NASA’s Lunar Rover was outfitted with four 9-by-32-inch tires consisting of steel-mesh toroids attached to aluminum hubs. The treads were made of V-shaped titanium which undoubtedly were considered the best type of tread for driving around on moon dust.
Back on Earth, the Tweel was developed
Back on earth, the concept of an airless tire became a serious concept once again when Michelin designed the “Tweel” in 2005. The Tweel consists of a thin rubber tread band reinforced by a composite-plastic belt and supported by dozens of V-shaped polyurethane spokes. Introductory claims versus conventional pneumatic radials were impressive. Studies showed that they were capable of two to three times the tread life and five-times-better lateral stiffness. Frankly, the Tweel seemed like the answer to every handling engineer’s dreams.
Holt Fiat of Fort Worth, TX explains that Bridgestone presented an airless tire concept at the 2011 Tokyo Motor Show. Mimicking the Tweel, the airless Bridgestone consists of a thin rubber tread supported by flexible thermoplastic spokes and a rigid aluminum hub. Inner and outer spokes run in opposite directions to provide vertical compliance without twisting. Bridgestone claims that high-speed noise and vibration are not concerns.
Airless tires are still years away
Despite plenty of R&D, nonpneumatic tires are realistically a decade away. Beyond their performance, two things will propel them toward acceptance: Tire companies must address the recycling of such tires and, of course, expense. The new wheels must be cost competitive with the old technology or the industry will likely stay with what is standard and familiar.