In one embodiment of the invention, a speed changing device located between the drum and spindle drives of a cotton picker row unit provides a variable ratio spindle-to-drum speed so that ground and spindle speed can be optimized to match field conditions. An automatic transmission with one or more shift points provides a plurality of gear ratio combinations to optimize spindle speed while ideal harvester ground speed for the prevailing crop conditions is maintained. Shift point selection provides downshifting when the spindle speed begins to exceed the desired maximum RPM and upshifting when the speed drops below a minimum RPM. Alternatively, a compact idler gear arrangement located between the drum and spindle drives on the row unit is shiftable to change the ratio of spindle speed to drum speed without affecting drum speed to ground speed synchronization. In another embodiment of the invention, variable ratio between the drum and spindle drives is provided by introducing an independent spindle drive train. The drum speed is synchronized to the forward speed of the harvester in the conventional manner, and the spindle drive maintains optimum spindle rotational speed independently of the drum speed changes. A further embodiment utilizes a constant speed unit drive to maintain spindle speed within the optimum range, and a gear change in the drum drive gears provides drum synchronization.