Makers of hybrid and electric cars are interested in the latest tire technology, not only to save weight but to reduce rolling resistance. For the last few years this meant tires that were a little too narrow and stiff, as automakers sought to squeeze out an extra fraction of one mpg wherever they could find it. Indeed, the one ingredient of tire technology that has not changed for decades, even as tire technology itself races ahead, has been the fact that they’re still filled with air. Automakers are well on their way to getting rid of spare tires to cut down vehicle weight — almost a third of all new cars now come without a spare — and some are already looking beyond run-flat tires that migrated over from the armored car cottage industry over a decade ago.
Toyota, along with a number of tire manufacturers, is already looking beyond runflat technology, and this is why the automaker showcased airless tires on its Fine-Comfort Ride concept at the Tokyo motor show last week, which is an adventurously styled MPV filled with a technologies that are just over the horizon.
The concept wore prototype Sumitomo airless tires, Bloomberg reports, in which a band of rubber encircles a plastic-aluminum hub, providing support to the interior of the tire. The concept is a little different from the Gyroblade tires that Sumitomo is also developing, in which large rubber spokes in the interior of the tire provide the connection to the center hub. The tire maker has been testing airless tires in a number of kei cars and golf carts, but the obvious promise of such technology in hybrids and electric cars is due to the fact that it can shave 30 percent off each tire’s weight by 2025 at the current pace of development. That’s no small fraction, and it comes with the promise of finally letting go of spare tires altogether.
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How soon might we see airless tires on production cars? Wako Iwamura, who heads the five-year airless tire project at Sumitomo Rubber, told Bloomberg that his target is 2020 for commercial sales.
While Sumitomo engineers expect significant weight savings with the first commercially offered airless tires, some work remains to be done on the aspect of rolling resistance: Iwamura estimates that airless tires offer 10 to 20 percent worse rolling resistance than traditional pneumatic tires, which is crucial for hybrids and electrics. This means engineers will have to find a way to give these tires a relatively rigid overall structure but the same level of damping as pneumatic tires used by hybrids and electrics, which will permit them to rotate at various speeds without deforming and without slowing the car down.
That’ll be the real test for airless tires: Will their internal structure be able to perform consistently at city and highway speeds for tens of thousands of miles? Sumitomo hopes to have the answer by 2020.
