This is a reply to the question about the X-type frames used by General Motors in the late ’50s and ’60s (Apr. 1). The X-type frames in question consisted of a large center “X” with no middle side rails. The thought behind it was a way to lower the car floor and, thus, the overall height of the car. It was referred to as a tubular frame, and it consisted of heavy box-section members. To protect in side-impact collisions, the floor pan and rocker panels
