Abstract: A chassis dynamometer designed for effectively performing bench testing performance of an automotive vehicle, comprises a first roller supported on a swingable shaft and housing therein stator and rotor forming a dynamometer, a second roller coupled with said first roller for synchronous rotation therewith; a flywheel detachably and coaxially disposed within the interior space of the second roller for rotation therewith; and a retainer associated with said flywheel, for detachably retaining said flywheel within the interior space of the second roller, the retainer restricting axial displacement of the flywheel relative to the second roller.