The frame number is located in different places on our cargo bikes and trailers. On the trailers, the frame number is knocked into the side of the base frame. On the yellow galvanized steel frames, we have knocked the frame number into the left side of the plate that sits between the top and bottom tubes. On aluminum frames for rearDrive or frames for cargo bikes without a motor, the frame number is stamped on a plate under the bottom bracket. On midDrive aluminum frames, the frame number is stamped on the seat tube just above the motor housing.