I'm not sure, but they may have made a special shim to fit under the derailleur clamp. I know Campagnolo made one to fit under the pump umbrella clamp when mounted on the top tube, and it seems like I remember something similar that was made by Simplex
"Bicycle Mark" Perkins Fresno Cycling Club - Historian Fresno, California, U.S.A.
On Mon, 17 Mar 2003 09:55:48 -0800 (PST) wayofftheback
> Did Simplex make two different sized front derailleur
> clamps--one sized for the metric tubing and one for
> slightly larger 1 1/8" diameter seat tubes?
> John Taglia
> Chicago, Illinois