I can understand frame flex, especially around the bottom bracket shell........even my 52/53cm frames will experience derailleur rub from time to time, especially when I climb out of the sadde to hammer.....in which case I ease out on the outer limit screw which sets the derailleur cage further out. That always eliminates this problem.
You can also spread open the derailleur cage a tiny bit to allow more clearance for this lateral chainring movement...
Last edited by roadfix; 04-21-06 at 07:34 PM.