An adapted test rig for fatigue tests of convertible roof systems has been developed for fatigue tests on servohydraulic four-poster systems. By controlling stiffness and masses the test rig allows to adjust the eigenfrequencies and eigenmodes of a convertible roof system embedded in a body in white. Thus, fatigue tests of the roof systems can be conducted in an early phase of product design. The test rig can be adopted to a broad variety of car geometries and roof types.