Grounding Electric bike

The answer to this is not clear cut. The purpose of "grounding" is generally to prevent shock in a situation where current may be exposed to an individual. Generally the frame of a vehicle is attached to the negative connector of the battery. This means all the electrical components can be attached to the frame as a negative voltage reference and only run positive wires to components. Should you ground your bike? well, if your motor, controller and battery system advise this, yes, but be very sure no positive wires could possibly contact your frame or you'd have a dead short, which could damage everything, including you if the short persists long enough. Some controllers may be blown by chassis grounding them! As small a device as a bike is, you are probably better off NOT grounding, but only completing what wires are needed for the circuits. Depending on the motor design, it may already be grounded by the mount to the wheel supports. The best answer I can give is fully read and understand the manuals and documents for your system ,and follow them to the letter, for best results, unless qualified electrical knowledge and experience overrides.