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Goodyear has developed a self-inflating tire, reports Steven Ashley in The New York Times (1/6/13). Designed for commercial trucks, it “automatically keeps tires inflated without the need for electronic controls or external pumps. The key is a clever pumping device — essentially a flexible tube nestled inside the tire — that operates much the same way a person’s muscles push food through the digestive tract in continuous pulses. As the tire rotates, high pressure caused by the vehicle’s load compressing the tire repeatedly deforms the embedded tube, generating a pumping action.” (image)

“If the pressure inside the tire falls below the required level, a regulator lets outside air into the pumping tube, where it is pressurized and sent through a valve into the interior cavity of the tire. And all of this happens automatically, without any action by the driver.” The result is improved fuel efficiency and less wear on the tires. Michelin, meanwhile, has been developing The Tweel, a tire that requires no inflating at all, since 2005. The Tweel features “flexible polyurethane spokes that support an outer band of tread material.”

The drawback is that it “vibrates considerably above about 50 mph.” Bridgestone also has its “Air-Free Tire,” a prototype design constructed of “thermoplastic ribs,” but it’s only suitable for golf cars, lawnmowers and the like. And Yokohama Rubber has developed a full-size “nonpneumatic concept car-tire called the Youmyaku, featuring “a honeycomblike network of curving flexible ribs around a large metallic hub.” No self-inflating or air-free tire is yet suitable for passenger cars, although Goodyear is reportedly looking into developing its “Air Maintenance Technology” for the consumer market.