Much of that comes down to combining nine speeds with a relatively low - powered engine, the transmission continually changing to optimal gears for the engine speed. (cnet.com)
Select optimal gear from your inventory for any class or job with the simple press of a button! (ggsgamer.com)
Due to the versatility of this design, all that is required is a simple internal 3 - speed hub to ensure optimal gearing with minimal changes. (treehugger.com)