The present invention is a device for increasing the stiffness of a pivot bearing assembly generally employed along with an actuator assembly of a magnetic disk drive. More specifically, bearing cartridges generally used in the art, are modified with a smaller spacer and a stiffener that is associated with the shaft. This modification reduces the rotating mass of the actuator assembly and increases the stiffness of the pivot assembly about which it rotates, thereby yielding greater system performance by increasing a critical resonance mode frequency.