When I first read that the first airless bike tire had just been created I had to laugh a bit. As a kid I had a bike with two solid (hard) rubber tires. It rode like crap, but guess what it had airless tires. Now that I have cleared up that little inconsistency, on to this cool airless tire tech dubbed the Energy Return Wheel.
The Energy Return Wheel works by using two steel rings that are suspended by a bunch of springs. This means that you can adjust how springy you like your ride.