Koni FSD (Frequency Selective Damping) patented technology provides a firm ride on long bumps and corners for control, and a soft ride on expansion joints and rough roads for comfort. This damper should significantly improve ride quality on your X3 without sacrificing handling.
The FSD has an extra valve that controls an oil flow parallel to the piston assembly that opens over high frequency inputs, such as expansion joints, providing a smooth ride. The valve closes over low frequency inputs such as cornering transitions, providing better control. The valving is integrated into the strut, is non-electronic, and does not require any external sensors or adjustments.