I'm using a Staton Inc system. Recently installed a custom built freewheel (34, 28, 24, 20, 16). The bike is fully automatic; it shifts gears by itself. I currently have the only gas bicycle in the world which shifts gears automatically through a shift kit. The gas tank is a see through tank. Therefore all I need to do is merely look down to see how much gas I have. I couldn't do that if the tank was behind me.