Thanks Strong Bad, DRONE, claude stanley, LBS-USA for your tips and hints. My question was just about which one is the best, a welded or a bolted connection, not a welded or a bolted side car. The tub is to be connected to a transalp 600 on the right side. I guess the frame of the transalp is made of ordinary steel. As you can see, the chassis tube is just behind the exhaust pipe.