A bicycle transmission assembly that is mountable to a bottom bracket shell of a bicycle frame. The bicycle transmission assembly includes an input crank assembly, an output chainring, a planetary gear mechanism, a control system and a mounting system. The planetary gear mechanism is mounted coaxially about an axis of the bottom bracket shell and provides a plurality of transmission paths. The control system is operatively connected to the planetary gear mechanism for selecting one of the transmission paths. The mounting system mounts the planetary gear mechanism and the control system to the bottom bracket shell. The mounting system includes at least one attachment point disposed on at least one frame boss extending radially outwardly from the bottom bracket shell. The control system is mounted nonrotatably to the at least one attachment point.