Abstract: A vehicle suspension more particularly for three pairs of ground-engaging wheels at the back of a semi-trailer. The axle of each wheel is carried by the free end of a crank arm pivoted intermediate its ends to a support member secured to and projecting underneath the semi-trailer chassis. The other end of each crank arm is pivotally connected to the piston rod of a single-acting hydraulic cylinder and piston unit, the cylinder of which is pivotally connected to a support secured to the vehicle chassis. All the cylinders of the units on one side of the trailer chassis are interconnected by flexible hydraulic tubing. The set of units on one side of the semi-traler are not connected to the set of units on the other side of the trailer and the wheel axles on one side of the trailer are independent of the wheel axles on the other side of the trailer. A predetermined amount of hydraulic fluid fills the cylinders.