the pivot shaft 94a with only a slight vertical movement transmitted to the axle 88 through the beam 90a likewise when the wheel 76a encounters the same obstacle as shown in fig1 b the beam 92a will rotate clockwise about the pivot shaft 94a barely inducing vertical movement to the axle 88 finally when the wheel 78a moves over the obstacle as shown in fig1 c the wheel 78a will cause beam 90a to rotate about the axle 88 without providing much vertical movement to the axle 88 on which the tank 16 and the chassis 80 are supported since the beams 92a and 90a are independent of the beams 92b and 90b the tandem wheels will operate independently on either side of the trailer also incorporated in the suspension is a trailing wheel articulation system which is responsive to the direction of movement of the tractor vehicle pulling the trailer referring now to fig1 a 17 18 19 and 20 the articulation of wheels 78a and 78b is provided as being at the ends of the beams 90a and 90b a chassis beam 104 extends between the ends of beams 90a and 90b and mounts bearing brackets 103a and 103b which subtend hinge pins 100a and 100b to which bearings 99a and 99b are journaled the wheel axles 102a and 102b are fixed to bearings 99a and 99b a link 106 extends between brackets 108a and 108b which extend rearwardly from bearings 99a and 99b so as to complete a parallelogram link 106 is connected to the.