Commercial vehicle seat with a securing unit in case of an overload of the rotating adjustment device

The seat (1) has a substructure (7) including an adjustment device with fixed and rotating portions for rotating a seat portion (2) relative to a body (8) with a bearing assembly. The assembly includes ball rings arranged relative to ball tracks between the fixed portion and the rotating portion so that the rotating portion is movably supported against the fixed portion. An overload protection unit includes stationary support elements by which the rotating and fixed portions are supported against each other if viability of one of the ball tracks reaches or exceeds critical deformation value.