Air suspension system

An air suspension system for a multi-axle vehicle having air bags (4,5; 6,7; 8,9; 10,11; 44 to 49) supporting either side of the axles (2,3; 41 to 43), including separate air lines (18 to 25; 50 to 55) respectively connecting each air bag to a level control valve (16,17; 56,57) via manifolds (26,27; M) and air lines (28,29; 54,55) to independently control air supply to the bags on either side, the separate air lines being of the same size and length to ensure that substantially the same volume of air is supplied to each bag to improve the responsiveness and stability of the system.