Apparatus for a manually-powered wheelchair comprising a frame and first and second wheel rotatably coupled to the frame. Each wheel includes a hand rim and a drive wheel. For each of the first and second wheels, a multiple speed transmission coupled to the wheel comprises a transmission output coupled to the drive wheel, a transmission input coupled to the hand rim, and at least two gears selectively coupling the transmission output to the transmission input. The transmission allows the drive wheel and the hand rim to rotate concentrically with one another but at different speeds. A selector is provided for selecting one of the at least two gears. A controller controls the selector to operate the transmission for the first and/or second wheel.