A typical bicycle tire puts about an inch of rubber on the road at a time. That works in dirt, but it´s not nearly enough tread to get a grip in deep powder. With the Ktrak aftermarket kit, your mountain bike floats above the snow and weighs only five pounds more. $540;
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.