An improved strain wave drive system employs an outer circular spline part and an outer dynamic spline part spaced apart by a gap from each other in a widthwise (axial) direction and each having a array of internally facing gear teeth, a two-part inner flexible spline (flexspline) having two different sets of externally facing toothed projections offset by a gap from each other across a width extending in a widthwise (axial) direction, a wave generator coupled to the central rotor or shaft for generating a wave impulse that displaces the inner flexspline toothed projections into mesh with those of the outer circular spline part and an array of roller bearings supporting an inner surface across the width of the flexspline in rolling line bearing contact.