Abstract: A vehicle suspension system has a gas-spring hydraulic strut for each of its four wheels. Each liquid actuator chamber of the struts at one end of the vehicle is connected to further chamber in the in the diagonally opposite strut, which further chamber acts in the opposite direction to the actuator chamber of that strut. A linear potentiometer within each strut provides a signal representative of the strut length to an on-board computer, which, when it detects a difference in the signal from any strut sensor from a predetermined value, causes a proportional servo-valve to admit hydraulic liquid from the actuator chamber of that strut at a flow rate proportional to the detected difference to return the strut length towards its predetermined value.