Abstract: A concrete finishing trowel includes a frame, a power source supported on the frame and having an output shaft, at least one rotor assembly supported on the frame. Each rotor assembly comprises a driven rotor shaft with a plurality of trowel blades extending outwardly therefrom so as to rest on a surface to be finished and to rotate with said driven rotor shaft to finish a respective circular area. A transmission system operably couples the power source output shaft to the driven rotor shaft of the at least one rotor assembly. The transmission system includes a variable driving pulley operable coupled directly or indirectly to the power source output shaft and including a resiliently deflectable portion that is movable to change the effective drive diameter of the variable driving pulley, and a variable driven pulley operably coupled to the variable driving pulley with a belt.