An undercarriage of a rail vehicle having a hydromechanical wheelset control system for a rail vehicle, comprising: a control valve a leading wheelset; and a trailing wheelset that is arranged in a direction of locomotion behind the leading wheelset, wherein the leading wheelset is adapted to vary its position in an arc of a rail pair interacting with it; a wheelset control is provided that is connected to the leading wheelset and to the trailing wheelset and that is adapted to hydraulically deflect the leading wheelset in dependence on a deflection of the trailing wheelset via the control valve, preferably by the same amount as the trailing wheelset, but in the opposite direction. characterized in that the control valve a) is mechanically or electromechanically actuable by a deflection of the trailing wheelset to bring the control valve into a deflection position that has the result of hydraulically deflecting the leading wheelset in the opposition direction to the trailing wheelset; and b) is mechanically or electromechanically actuable by a deflection of the leading wheelset to bring the control valve into a blocking position that stops a hydraulic deflection of the leading wheelset on reaching the desired deflection. preferably wherein c) the pump is switched into an idling state in the blocking position so that no power losses occur; and in that the mechanical actuation of the control valve for moving into a deflection position takes place via a first push-pull cable and for moving into a blocking position takes place via a second push-pull cable, wherein the first push-pull cable reproduces the displacement angle of the trailing wheelset with respect to the undercarriage frame and the second push-pull cable reproduces the displacement angle of the leading wheelset with respect to the undercarriage frame, preferably in that the respective push-pull cable (9, 10) is coupled to an actuation cylinder of the associated wheelset (2, 3). a control valve a leading wheelset; and a trailing wheelset that is arranged in a direction of locomotion behind the leading wheelset, wherein the leading wheelset is adapted to vary its position in an arc of a rail pair interacting with it; a wheelset control is provided that is connected to the leading wheelset and to the trailing wheelset and that is adapted to hydraulically deflect the leading wheelset in dependence on a deflection of the trailing wheelset via the control valve, preferably by the same amount as the trailing wheelset, but in the opposite direction. characterized in that the control valve a) is mechanically or electromechanically actuable by a deflection of the trailing wheelset to bring the control valve into a deflection position that has the result of hydraulically deflecting the leading wheelset in the opposition direction to the trailing wheelset; and b) is mechanically or electromechanically actuable by a deflection of the leading wheelset to bring the control valve into a blocking position that stops a hydraulic deflection of the leading wheelset on reaching the desired deflection. preferably wherein c) the pump is switched into an idling state in the blocking position so that no power losses occur; and in that the mechanical actuation of the control valve for moving into a deflection position takes place via a first push-pull cable and for moving into a blocking position takes place via a second push-pull cable, wherein the first push-pull cable reproduces the displacement angle of the trailing wheelset with respect to the undercarriage frame and the second push-pull cable reproduces the displacement angle of the leading wheelset with respect to the undercarriage frame, preferably in that the respective push-pull cable (9, 10) is coupled to an actuation cylinder of the associated wheelset (2, 3). the control valve a) is mechanically or electromechanically actuable by a deflection of the trailing wheelset to bring the control valve into a deflection position that has the result of hydraulically deflecting the leading wheelset in the opposition direction to the trailing wheelset; and b) is mechanically or electromechanically actuable by a deflection of the leading wheelset to bring the control valve into a blocking position that stops a hydraulic deflection of the leading wheelset on reaching the desired deflection. a) is mechanically or electromechanically actuable by a deflection of the trailing wheelset to bring the control valve into a deflection position that has the result of hydraulically deflecting the leading wheelset in the opposition direction to the trailing wheelset; and b) is mechanically or electromechanically actuable by a deflection of the leading wheelset to bring the control valve into a blocking position that stops a hydraulic deflection of the leading wheelset on reaching the desired deflection. preferably wherein c) the pump is switched into an idling state in the blocking position so that no power losses occur; and in that the mechanical actuation of the control valve for moving into a deflection position takes place via a first push-pull cable and for moving into a blocking position takes place via a second push-pull cable, wherein the first push-pull cable reproduces the displacement angle of the trailing wheelset with respect to the undercarriage frame and the second push-pull cable reproduces the displacement angle of the leading wheelset with respect to the undercarriage frame, preferably in that the respective push-pull cable (9, 10) is coupled to an actuation cylinder of the associated wheelset (2, 3).