typically bobbers have the tins cut and other things removed/modified like lights, bars, seats, exhaust, wheels, front ends...basically the frame is left unmodified. Choppers usually contain a modified frame. Doesn't mean that it has a hardtail/rigid or long front ends. Kinda like calling an oil bag an oil tank. Basically the same thing as they do the same job. Oil bags hang off the side, oil tanks are inside the frame somewhere.
