The supporting device of the semi-trailer, commonly known as the leg, is installed in the front of the semi-trailer and plays the role of supporting the semi-trailer. The front height of the semi-trailer can also be raised and lowered by the hand drive mechanism of the supporting device to facilitate the connection and disconnection of the tractor. The support device needs to be retracted when in operation.

① Requirements for supporting devices:

(1) The semi-trailer can be reliably kept in a horizontal position when unhanging;

(2) When unhanging and connecting, it can be quickly lifted and lowered, and its height can be easily coordinated;

(3) Simple structure, sufficient strength and support stiffness.

② Classification of supporting devices

(1) According to the mode of operation: there are linkage supporting devices and single acting supporting devices. The former only needs to be operated on one side to make both sides of the support device lift at the same time, while the latter needs to be operated separately on both sides, and now there are high-end electric lifting support devices, which can greatly save the driver's physical consumption and improve the efficiency of hanging.

(2) According to the cross-section shape of the supporting tube: round tube, square tube, octagonal tube support.

(3) According to the gear transmission mechanism: there are single stage, double stage and three stage gear transmission supports.

(4) According to the structure of the supporting tube: there are basic and folding supports, the former supporting tube can not be folded.

(5) According to the form of the supporting foot: there are articulated, rubber pad, ball Hank and roller type supports.