Originally Posted by
joejack951
The interface may be the same but the extension part of the stem is quite different. A threadless stem uses a large diameter tube while the quill stem uses a smallish, solid shank. On a long reach stem, the difference in stiffness could be quite noticeable.
Good point. I've had quill stems on old road bikes where the flex was quite visible. It was obviously twisting on the horizontal plane rather than bending vertically. Never seen (or felt) anything like that, even with really cheap threadless stems.