I donâ€™t think this is right, but I used up so much B vitamins that I could not figure it out. And it is probably back words for a mathematician. So how do I figure out a tow or three stage gear reduction for a bicycle that will bring the peak efficiency rpm down to a legal speed? I write math visually, and canâ€™t understand it, unless it produces a logical number. 3000rpm x (3â€pulley/12â€) x (3â€/12â€) = rpm x 1036.828milimeters, circumference of 26â€ tire /80467.2 millimeters per mile= mph?