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 input crank assembly is mounted
to a rotatable crank axle mounted to the bottom bracket shell. The
planetary gear mechanism is mounted to the bottom bracket shell and
provides a plurality of transmission paths. The planetary gear mechanism
includes a sun gear, a ring gear and a locking element operatively
connecting the sun gear and the ring gear. The control system is
operatively connected to the planetary gear mechanism for selecting one
of the transmission paths.