An arrangement for a terrain-going motor vehicle that has a chassis with a forward wheel axle with a driving pair of wheels (12:1) and a rear wheel axle with a driving pair of wheels (13:1), a half-track unit (15:1, 15:2) arranged at any one of the of said driven wheel axles (12, 13) with parallel half-track assemblies located at a distance from each other that interact with the ground on which the motor vehicle is being driven, characterised in that each half-track assembly comprises: a pivotable arm that supports at one of its ends a tracker wheel, and that is so mounted to pivot attached through a joint at the chassis at its other end that the tracker wheel can pivot in a vertical plane central to one of the driving wheels (12:1; 13:1) of the wheel axle, a continuous track arranged to run around the tracker wheel and the driving wheel (12:1; 13:1) of the wheel axle, a hydraulic system including a piston-cylinder device that can be set into alternative conditions through the influence of a hydraulic medium under pressure and which piston-cylinder device is united at one end to the chassis through a joint and united at the second end with the pivotable arm for the setting of the latter into angular positions (α) that include not only an inactive position directed upwards from the ground, but also an operating condition directed downwards towards the ground, a positional valve that can be set into different operating conditions, which valve when set to: a first operating condition allows hydraulic medium under pressure to be led to the piston-cylinder device for the setting of the pivotable arm and thus also the tracker wheel to the lower operating condition and in interaction with the support, a third operating condition allows hydraulic medium under pressure to be led from the piston-cylinder device for the setting of the pivotable arm and thus also the tracker wheel to the upper inactive position and away from interaction with the ground, whereby the tracker wheel is placed in the first operating condition in contact with the ground at a pre-determined force that is determined by the selected internal pressure of the hydraulic medium. a pivotable arm that supports at one of its ends a tracker wheel, and that is so mounted to pivot attached through a joint at the chassis at its other end that the tracker wheel can pivot in a vertical plane central to one of the driving wheels (12:1; 13:1) of the wheel axle, a continuous track arranged to run around the tracker wheel and the driving wheel (12:1; 13:1) of the wheel axle, a hydraulic system including a piston-cylinder device that can be set into alternative conditions through the influence of a hydraulic medium under pressure and which piston-cylinder device is united at one end to the chassis through a joint and united at the second end with the pivotable arm for the setting of the latter into angular positions (α) that include not only an inactive position directed upwards from the ground, but also an operating condition directed downwards towards the ground, a positional valve that can be set into different operating conditions, which valve when set to: a first operating condition allows hydraulic medium under pressure to be led to the piston-cylinder device for the setting of the pivotable arm and thus also the tracker wheel to the lower operating condition and in interaction with the support, a third operating condition allows hydraulic medium under pressure to be led from the piston-cylinder device for the setting of the pivotable arm and thus also the tracker wheel to the upper inactive position and away from interaction with the ground, whereby the tracker wheel is placed in the first operating condition in contact with the ground at a pre-determined force that is determined by the selected internal pressure of the hydraulic medium. a first operating condition allows hydraulic medium under pressure to be led to the piston-cylinder device for the setting of the pivotable arm and thus also the tracker wheel to the lower operating condition and in interaction with the support, a third operating condition allows hydraulic medium under pressure to be led from the piston-cylinder device for the setting of the pivotable arm and thus also the tracker wheel to the upper inactive position and away from interaction with the ground, whereby the tracker wheel is placed in the first operating condition in contact with the ground at a pre-determined force that is determined by the selected internal pressure of the hydraulic medium.