The invention relates to a pneumatic diaphragm brake cylinder (1 ) for motor vehicles, with a housing part (6) on the pressure side and a housing part (2) facing away from the pressure side, as well as a diaphragm (24) arranged therebetween, which divides the interior of the diaphragm brake cylinder into two chambers (20, 31) sealed off from one another, of which a first chamber (20) comprises a pressure chamber loaded by a pneumatic pressure and a second chamber (31) comprises a piston chamber for a piston (26) actuated by the diaphragm (24), wherein a peripheral fastening edge (32) of the diaphragm (24) is clamped between the pressure-side housing part (6) and the housing part (2) facing away from the pressure, and wherein the pneumatic pressure loads a surface (50) of the diaphragm (24) which is effective with respect to a working movement of the diaphragm (24), and a reduction ring (36) is provided which extends axially from the diaphragm (24) into the housing part (2) facing away from the pressure and which radially reduces or radially limits the effective area (50) of the diaphragm (24), and at least the reduction ring (36) and the diaphragm (24) are designed as a one-piece component.