Rocket Sprocket

Here is a funny little idea. Rocket Sprocket, Sprock-O-Matic, made in Miami, Florida. It would turn your bike into a 2 speed, with the chainring being elliptical. Depending upon where the ellipse was, it would make it feel like you were riding in a harder or easier gear. It was a fad, like a mechanical Shimano Bio-Pace. It works on one-piece cranks, and the “pin” on the crank would migrate from one position to the other.


I assume it didn’t work well, that’s why it never took off. Oval chainrings surfaces in the bike world every few decades. We collect examples, including the Thetic, Durham, and ones made by Suntour and Shimano.


The earliest oval chainring we have is on a 1893 Columbia Model 32. it is a fixed gear with elliptical chainring and it rides like a dream.