Choosing a Small Sprocket
Chain Sprockets are effectively regular polygons. Because of this, when the small sprocket is pulling the chain a pulse is created in the system.
It is important not to choose a sprocket too small for the smoothest power transfer.
Most engineering manuals suggest that 17 teeth be a minimum for high speed systems.
This graph shows how the lower leverage postion compares to the higher leverage postion as the sprocket rotates. (pitch /(2*TAN(PI()/ teeth ))) / (pitch /(2*SIN(PI()/ teeth )))
For comparison purposes, here are many of the common bicycle and motorcycle sprockets.