I run a Schlumf Speed-drive on my GoBike, this is the middle of the range, fit a Mountain-drive if you find you are lacking gears low enough for steep hills, a Speed-drive if you want to add higher gears and a High-speed drive if you've got legs like tree trunks and want to tear up the tarmac at high speed! I still have not got the hang of changing up & down on the fly by the way, maybe with shorter cranks it would be easier (I have smallish feet). I'm thinking of changing to shorter cranks anyway (to help my knees)