An apparatus meant to be incorporated into a suspension system (1000, 2000) suspending a plant (i.e., an overall plant that includes a physical plant (110) and possibly a load that the physical plant supports) of a vehicle acts to alter the spring constant of at least one spring (155, 156) of the suspension system (1000, 2000) in response to changes in the weight of the plant so that a resonant frequency of the at least one spring (155, 156) isolating the plant from a jolt encountered by the vehicle during travel remains substantially unchanged despite changes to the weight of the plant.