20 mph. If you want to use it in a lightweight bike, the 48v 09 bottle battery with the included 20A sine-wave controller would make a very neat conversion. I have one of those kits. They're plug-and-play with waterproof connectors. The only thing I had to do was wire the speed sensor directly to the controller because my motor didn't have a speed signal wire. I'm not sure whether the Q100C has a speed signal wire.