Abstract: Springs of different types are provided with the ability to dynamically change stiffness. For one embodiment turning the elastic beams with elongated cross-section inside a leaf spring's housing plate, leaf springs stiffness is varied. Friction forces between plates are also controlled by using a thin layer of electro-rheological fluid between plates whose viscosity is greatly varied by application of voltage. Second embodiment springs made of hollow tubing filled with oil wherein inside pressure is changed by an actuated membrane or piston whose movement drastically increases the hydrostatic pressure inside the tubing and thus increases tensile stress in the tubing's wall and expands the diameter of tubing which may be of cross-section purposely suited for expansion, thereby increasing its stiffness or decreasing it with any desired frequency or changing the stiffness possibly in milliseconds for a period of time.