A truck trailer having a pair of tandem spaced apart rear axles and a suspension system for supporting the axles from the chassis of the trailer having a pivot member intermediate the axles about which the axles may pivot relatively to one another, the axles being connected to respective ends of leaf springs. The trailer has apparatus for lifting one of the axles relative to the other axle selectively so that the wheels carried by the lifted axle may be lifted off the roadway. The apparatus for lifting includes air bags which may be inflated by pressurized air or deflated to control the position of the axle to be raised. The air bags are positioned between one of the axles and the chassis and when pressurized air inflates the bags the other axle is lifted about the pivot member.