I bought a set of wheels from Stevil_Knevil. Per his suggestion, put on the Michelin moped tires. Put on a 180mm Avid disc. AND, unbelievably, when I bought some parts from MopedMart on ebay, MopedMart threw in a bunch of extra parts, one of which was the rear sprocket!
MopedMart has much of the original Voloci MOPED parts and he is currently listing forks, rear shock, mirrors, handlebars, turn signals, etc.
MopedMart gave me the sprocket and probably has more sprockets (my guess). He has Voloci wheels and seats and some other Voloci parts that he isn't advertising on ebay. Might be worth an ebay reply to him if you need Voloci moped parts (no controller, battery pack, wire harness, etc.).
I originally bought the Voloci wheels thinking I would rebuild the rear wheel as an electric hub motor but have since changed my mind.
Now, my plan is to make a 48V NiMH pack to fit in and slightly above the stock frame, then a >48V controller and CycleAnalyst to modify the single-magnet Voloci Hall throttle to work with the after-market controller.
I am thinking I do the electrical connections under the stock Voloci controller cover. I think/hope I can fit a 48V to 12V down converter in there too, but if not, I will mount the downconverter under the seat.
My goal is nearly stock (battery will stick out of the frame by about 2 inches, the after-market controller will be on the seat stays, to the rear, and wires run into the motor controller area where the stock wires used to enter that area). I'd like a bit more zip and 25% more Voltage should do that. I would like to be closer to 30 mph than I was at 36V.
I fried my Voloci controller and there are no more to be had, so time to update the technology.