Checkout this video of the Energy Return Wheel from Britek Tire and Rubber. It is an airless bike tire that is also supposed to be more efficient when compared to a traditional bike tire.
Here is another video that will give you a little more technical info on how the Energy Return wheel works. The video talks about wheels for cars and trucks but the principal is the same for the their bike tires.
Here is a little more info from Briteck:
“The physics behind the ERW is similar to that of a garage door. Even though a garage door weighs several hundred pounds, when it is sprung by the use of springs, it becomes de-weighted. So when you lift it, it only feels like it weighs a few pounds. In summary, an object that is sprung requires dramatically less energy to move than an unsprung object. In addition to the use of springs, an object can be sprung by stretching rubber. Scientists call this “Elastic Potential Energy.” At the center of the ERW is a layer of rubber. Through the use of adjustable rods, the rubber is stretched which stores elastic potential energy in the wheel, turning the ERW into a 360-degree slingshot that retains energy (hence the term “Energy Return Wheel”). When the ERW is attached to an object, that object becomes sprung. Just like a garage door that is sprung, the attached object becomes de-weighted and requires dramatically less energy to move than an unsprung object. Less energy to move means an increase in efficiency.”
Apparently the ride feel can be adjusted via the screws in the wheels.
I hope to have more detailed info about this new bike tire and wheel technology soon.