The secondary couple components in the plane containing both axes of a constant-velocity joint (CVJ) are T tan (θ/ 2) ( T ; torque, θ ; operating angle) and the components perpendiculer to the plane are zero, if the friction in a CVJ is not taken into account. The secondary couples of a real CVJ are thought to be considerably affected by the frictional forces acting in it. The authors constructed a system by which to measure the secondary couple transmitted to the bearing of a CVJ shaft and initiated the study of the secondary couples of an actual CVJ. It is shown that the effects of the frictional forces on the former secondary couple components are related to the torque loss of a CVJ and that the torque loss can be calculated from the measured values of the component using a simple equation. It is also shown experimentally that the latter components exist but are small compared with the former components.