Electric and fuel-cell carmakers dream of an airless tire

A lawnmower's airless tire deforms as it rolls over a curb.

A lawnmower's airless tire deforms as it rolls over a curb.

Toyota debuted a new hydrogen fuel-cell concept car, the Fine-Comfort Ride, at the 45th Tokyo Motor Show that wrapped up yesterday. The Fine-Comfort Ride signals Toyota’s ongoing commitment to fuel-cell vehicles—the company still believes that fuel cells will eventually beat electric batteries on cost. Even though Toyota insists on going its own way on emission-less cars, they showcased one piece of technology that should also appeal to electric car makers trying to save weight: Sumitomo’s prototype airless tires. Sumitomo’s prototype is essentially a band of rubber wrapped around a plastic-aluminum hub and has already been tested on golf carts and small Japanese kei cars

Toyota and Sumitomo still have to solve some problems before the tires will be commercially viable: right now the airless tire prototypes weigh about the same as their air-filled cousins and still have 10-20% more rolling resistance than air-filled tires. Rolling resistance refers to the force resisting motion when a body rolls on a surface. One major factor contributing is the deformation of the wheels—imagine a typical pneumatic tire with too low pressure flattening as it meets the road, increasing the size of the contact surface and thus increasing the rolling resistance of the tire. 

Rolling resistance is why properly inflated tires help save fuel costs, and it explains why airless tires, which exhibit much more deformation, have not been introduced to the market yet. Until airless tires weigh less than traditional pneumatic tires and have comparable rolling resistance, makers of fuel-cell and electric cars will not see any performance gains by switching to them. At the Tokyo Motor Show, Toyota’s chief engineer Takao Sato said he expects to shave enough weight off the airless tires to make them comparable to pneumatic tires by 2025.

Sumitomo’s airless concept joins a select group of tire-makers developing airless car technology—Michelin introduced its Tweel airless tires in 2005, and started selling them in North America for steer-skid loaders in 2012. In 2015, Hankook introduced their 5th airless tire prototype, the iFlex. In 2013, Bridgestone unveiled their second generation ‘Air Free Concept (Non-Pneumatic) Tire’. Polaris has sold its TerrainArmor airless tire with its ATVs since 2013, boasting that it can take a .50 caliber round and drive another 350 miles.

So far, airless tires have seen use in specific industrial and commercial applications where the vehicle lacks suspension such as a lawnmower or skid-steer loader, where the vehicle is exceptionally light, like a golf cart, and is able to avoid serious tire deformation, or where the vehicle is extremely heavy and needs to avoid punctures while traversing a job site. 

The most farsighted concept in the airless tire space is Michelin’s new 3D-printed prototype that combines wheel and tire in one, nicknamed ‘The Vision’. The tire features a psychedelic, blue-webbed structure and is composed of organic, recyclable materials, with orange zest instead of petroleum being used for the resin. The reloadable tread band can be easily retreaded with custom patterns—for snow or sand, for instance—with a 3D printer and has embedded sensors that collect diagnostic information for the driver. 

Watch the video below to see how this futuristic wheel-tire combination might work:

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