Abstract: A frame for attaching a side car to the frame of a motorcycle. The attachment frame includes parallel upper and lower rails which are connected at their front ends to the motorcycle frame by a parallelogram linkage for simultaneous tilting movement of the front portions of the attachment and motorcycle frames. The rear portion of the attachment frame is pivotally connected to an auxiliary wheel which is disposed beneath the attachment frame directly adjacent to the motorcycle. The attachment frame carries means for connecting a side car outwardly from the attachment frame and auxiliary wheel. The connection between the rear portions of the frames comprises a roller mounted for movement along a normally vertical track to provide independent movement of the frames and form an axis for tilting movement of the attachment frame. An air cylinder provides adjustable support for the load carried by the attachment frame.