Abstract: The invention is a commutator for a high speed, high power DC traction motor having a rotor with a plurality of copper commutator bars having a V-shaped groove an axial end thereof, an electrically conductive retaining ring engaging the V-shaped grooves of the commutator bar, and means for exerting an axial force between the retaining ring and commutator bars to retain the latter against radial movement during high speed rotation of the rotor. Each of the commutator bars has an axial end face with a radially inwardly extending axial depression which joins an axially extending radial depression in a radially inner axial surface thereof adjacent the retaining ring. The retaining ring has an axial end face aligned with the axial end face of the commutator bars and an outwardly radially extending axial depression which joins an axially extending radial depression in a radially outer axial surface thereof adjacent the commutator bars.