Some people would be happy to come up with one revolutionary new bike design, but Mark Groendal, who created the “Slingshot” bike, has done it again: with a Flexible Down Tube for his “flexible flyer”, the Altercycle. These bikes have a curved downtube. So far, not that different. Because of its flattened, curved shape the down tube is also flexible. This flexible down tube is claimed to provide a subtle performance boost with each pedal stroke.