A bicycle rear wheel adapter has an annular body that abuts a sprocket-carrying body that extends in an axially outer direction and receives sprockets in radially peripheral positions. A coupling element on the annular body couples with the sprocket-carrying body so the adapter rotates as a unit with the sprocket-carrying body, and a sprocket-receiving seat on the annular body couples with a sprocket so the adapter rotates as a unit with the sprocket. The adapter is suitable for cogsets with small sprockets grouped in a monolithic grouping.