While bicycling doesn’t produce any pollution, every time you get a flat tire while out on a ride, that rubber tube ends up in a landfill. By one estimate, riders in San Francisco alone throw out more than 100,000 tubes every year, enough to wrap the Golden Gate bridge 33 times. The SMART Tire Company hopes to make flat tires, and all that rubber waste, a thing of the past, with airless bike tires that use technology originally invented by NASA.
NASA developed its airless shape memory alloy tires for use on its lunar and Mars missions; the tires are flexible like rubber, but can work on various terrains, can’t be punctured, and don’t use any air—perfect for allowing a rover to explore another planet without worrying about flats. The tires are made of a material called Nitinol, a combination of nickel and titanium. It’s getting its first consumer application through SMART’s bicycle tire called METL.
SMART has plans to make car tires, too, but it started with bikes because the regulatory requirements are lower than the automotive industry, which means they could see a faster time to market, and also because demand is high, says Brian Yennie, co-founder and CTO at SMART, over email. The tires won’t be “ultralight,” so road cyclists might not be interested, but their weight will compare to tires for gravel, mountain, and eBikes, he says. “We argue that there are externalized savings and benefits that increase the benefits beyond just weight,” he adds. “For example, for many cyclists simply ditching spares and repair tools saves more weight than the delta between tire models.”
In order to grip onto the ground, the tires have a tread around the alloy made from Polyurethanium, SMART’s “code name” for a proprietary, rubber-like material. Though riding may cause some of that tread to wear away, SMART says it will produced total waste—and need to be disposed of less frequently—than all the rubber that goes into regular bike tubes and tires. “We also intend to study the chemical composition and manufacturing process in order to lessen the total environmental impact at all stages of tire life,” Yennie says, and they’re working on ways to allow riders to get their METL wheels retreaded.
SMART expects the first METL bicycle wheels to be publicly available in 2022, and has also partnered with scooter company Spin to develop shape memory alloy tires for e-scooters. In the future, it hopes to tackle car tires, though it’s not the only one working on an airless alternative; Michelin says they’ll have an airless tire—called the Uptis, or Unique Puncture-proof Tire System—on the market by 2024.