Disc brake cylinder groove with a recess consisting of three sector surfaces

A disc brake with a brake caliper which straddles the outside edge of a brake disc and brake pads arranged on both sides of the brake disc and which is provided with a hydraulic actuating device, adapted to press the brake pads to the brake disc and having at least one brake cylinder and a brake piston axially, displaceable within the brake cylinder, an elastic sealing ring arranged in a surrounding annular groove inside the brake cylinder which rests frictionally for sealing purposes on an outside surface area of the brake piston, the annular groove having a groove wall nearest to the brake pads which is generally perpendicular to the brake piston axis and a surrounding recess adjacent to the brake cylinder, said recess receiving the sealing ring which is elastically pressed by the brake piston as the latter is axially displaced when the brake is applied, said recess having at least three adjacent surrounding conical surfaces the cross-sections of which are generally straight lines, with the angles of the straight lines towards the brake cylinder axis increasing progressively, starting from the surface which borders on the cylinder surface to the surface which borders on the groove wall.