When using a self-supporting wheel tractor body to build a tracklaying tractor, it is necessary to supplement the body of the tractor with a massive frame for spring mounting the running wheels. This frame has the disadvantage of considerably increasing the weight of the tractor and of making access to the tractor body difficult. It is proposed that the journal (49) of a tensioning wheel (50) carries a double-armed balance beam (51) whose lower arm (52) is mounted on a main arm (2) of the chassis and whose upper arm (53) is rotatively linked to a tension jack (54) arranged on the main arm (2). The running wheels (67, 68, 69, 70) are secured to the main arm (2) by means of rockers (3, 59) with primary springs (4) inserted between the rockers (3, 59) and the main arm (2). A secondary spring (5) is supported from above on the main arm (2) and secured to a console (6) arranged on the body (82) of the tractor. The axis of a drive wheel (7) is downwardly and backwardly oriented with respect to the axis of a countershaft (8) of the portalgear (9), and the axis of the countershaft (8) is downwardly and backwardly oriented with respect to the axis of a ring gear (10) of the bevel gear.