This is a reply for yesterdays post to Beamer. My back sprocket measures 6 inches across and I also measured a Mobylettes sprocket aswell and it measures roughly 7.5 inches across. The only idea I can come up with is to use a larger Motobecane sprocket from another model? My bike shop idea is a failure because of the drum brake centred in the sprocket. But from the looks of it they have a similar mounting pattern(Cady - MOby). The Cady has a 16' rim and the moby has a 17' rim so that might pose a problem. Maybe you could look into other motobecanes that run a 16' rim but have a higher top speed (model 40 or 50?). you can refernce the manuals at Moped riders Assoc. and they also have the owners manual of various models. If you want I'll count the teeth of the different peds but that'll have to wait till after work tommorow. Just reply if I can help you out or email me and I'll see what I can do!