Abstract: The invention provides a control system for a vehicle fluid spring suspension system consisting of four fluid springs which support the vehicle body from two longitudinally-spaced trucks. Typically such a vehicle is a rail car employing air springs. The two air springs on each truck are disposed on opposite sides of the longitudinal center line of the vehicle, corresponding to its direction of travel. Three of the springs are provided with levelling valves which keep them at a constant height. A measuring device, either mechanical or electrical, measures the difference in internal spring pressure in the two springs on one truck that both have levelling valves; it also measures the difference in internal spring pressures in the two springs on the other truck and then adjusts the pressure in the spring without a levelling valve until the pressure difference is the same as for the two springs on the other truck.