In order to improve a support unit for motor vehicles comprising a supporting structure mounted on a rear end portion of the motor vehicle a sensor unit is provided for detecting forces acting on the supporting structure and elastically deforming the same. The sensor unit is provided with a sensor base, comprising two fixation regions which are spaced apart and can be fixed to mounting regions of an elastically deformable supporting structure portion. A transformation region disposed between the fixation regions mechanically converts the movements of the mounting regions, and thus also of the fixation regions relative to one another. Movements are generated by the elastic deformation of the supporting structure portion, into a movement of measuring points of the transformation region relative to one another. The movement of the measuring points can be detected by the sensor unit.