When you’re exploring another planet, the last thing you want to have to deal with is tire damage when AAA is millions of miles away. It’s a concern that prompted NASA to develop an airless titanium tire that’s flexible like rubber, but nearly indestructible. As has been the case with many of NASA’s inventions over the years, that space age tire technology will soon be available to consumers.
Using air-filled rubber tires on a vehicle just isn’t a practical solution for exploring nearby celestial bodies whose natural terrain is covered in rocks and sharp objects. So for the handful of wheeled vehicles that NASA has sent to the moon and Mars, metal wheels are a better alternative. For the Lunar Rover, which Apollo 15 brought to the moon, wheels made of hollow metal springs were created that could absorb bumps to make the ride more comfortable for astronauts. But most metals lose their shape over time and become brittle when repeatedly flexed, resulting in misshapen wheels that don’t roll as well, and even worse, severe damage that prevents them from rolling at all.
As an alternative, NASA has spent several million dollars over the past seven years developing Nitinol: a metal alloy made of aluminum (Correction: March 17, 3:20pm: nickel, not aluminum) and titanium that behaves differently. Metal springs eventually lose their ability to spring back to their original shape because the bonds between their atomic structures become so stretched they’re no longer able to return to their initial arrangements. But Nitinol features a more ordered atomic structure and exhibits something known as the shape memory effect, which allows it to be deformed but return to its original manufactured shape again and again without permanent damage. It allows metal tires to be created that can deform to absorb the impact of uneven terrain like rubber, without the possibility of a flat tire occurring.
It’s incredible technology that will soon be available in the coming years for a vehicle that will probably never leave Earth’s atmosphere: your bike. A startup called The Smart Tire Company has announced that it’s creating a metal bicycle tire using NASA’s Nitinol alloy that never needs to be inflated, will never spring a leak, and will probably survive a lot longer than the bike itself.
Called the METL (Martensite Elasticized Tubular Loading) tire, its creators are hopeful it will be available as an alternative to premium bike tire options as early as 2022. It remains to be seen just how much a titanium alloy bike tire will cost, but you can assume that it will be a long time before kids find a bike with Nitinol wheels under the Christmas tree. For cyclists who are happy to spend tens of thousands of dollars on their bikes, however, the METL tires could be the last set they ever have to buy, although they’ll still require regular maintenance.
The most common problem with airless tires is that they often feature open structure designs that can allow debris to get inside and throw off the balance of the wheel. Using a structure made of metal instead of rubber further complicates things because the smooth finish means the tire doesn’t have much grip. To solve this, the METL tires will also be finished with a rubber-like tread made from a material called Polyurethanium that adds grip and makes them suitable for riding on all terrains, including pavement, gravel, and dirt. Over time the tread will wear out and need to be reapplied, but that maintenance is expected to be a lot cheaper than having to regularly replace a set of tires.
The METL tires won’t suitable for every rider. They are, after all, made of metal, and are expected to be heavier than the premium lightweight tires used by professional cyclists and athletes. But for most other applications, including athletes who use larger bikes on off-road terrains, the tires won’t feel any different during a ride.
The Smart Tire Company is making a lot of promises about the advantages of its Nitinol tires over rubber ones—see this extensive FAQ on its website touting the virtues of the technology—and there’s good reason to be excited about the technology. Obviously NASA felt it was important enough to spend millions of dollars on its development. But we’ve been promised airless tires for many years now, from industry giants like Bridgestone who have the manufacturing capabilities to make them a reality. They’re still not here, though, not even for bikes, which is just about the least demanding application for the technology.
There’s little doubt that one day flat tires will be a thing of the past, but will it be thanks to this startup’s efforts? If it can deliver the METL tires in the next couple of years as it intends to, there’s good reason for Michelin, Goodyear, and Bridgestone to be concerned.