In converting my Schwinn Le Tour increasingly more for commuting purposes, I'm going to use a flat bar and use 7-speed Shimano rapidfire brake/shift levers pulled from an old mountain bike.
Thing is, the Schwinn is one of those old ones that has a narrower internal head tube diameter requiring a narrower (21.15mm) quill stem. So I'm using an old Schwinn-specific SR forged quill stem, pictured here. The clamp diameter is correct - 25.4mm - but these old road quill stems don't have as wide of a clamp and may not support the bar as well when it is torqued side-to-side.
Any thoughts on this issue? I have no experience here, and don't expect for there to be a problem, but wanted to know if there's any reason this would be more flexy, or more likely to crack a lightweight aluminum bar.