Radially outer ring of a bearing unit for a hub-wheel assembly for motor vehicles, the radially outer ring being provided with: a flange portion having a plurality of axial fixing holes that connect an element of the motor vehicle wheel to the radially outer ring, an almost cylindrical portion which with part of its radially internal surfaces defines raceways for rows of rolling bodies of the bearing unit, an axially internal or axially external surface of the flange portion and a radially external surface of the cylindrical portion connected to each other by a first portion of toroidal surface (St1) and of a second portion of toroidal surface (St2) defined by corresponding first radius (R1) and second radius (R2), a truncated cone surface (Stc) defined by an angle (a) formed with a rotation axis (X) of the radially outer ring is interposed between the first portion of toroidal surface (St1) and the second portion of toroidal surface (St2).