I have a Jack Taylor 23" Touring frame built with 531 red label tubing. My riding partner from France loves to ride this bike when he is over here. We've had long conversations about thin wall tubing and how it can effect the ride. Jan is right there is a "planing" with the lighter tubes. Paul weighs appox. 170 and I'm at 185, the front derailer will rub on a hard climb but never shifts. Norman brass welded the frame, but I don't know if they used heavier stays or not. It's really a fun bike to ride. Take a look here:
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