Originally Posted by
daoswald
I would probably go back to the 27T (or maybe a 28T if one is made in the appropriate configuration). 28T is pushing things a little, but as I've discovered on my 105 RD it's workable. And then in front do as suggested, moving from a 30t small ring to a 26T or 28T. The problem here will be a matter of whether the FD can handle the tooth-difference between the smallest ring and largest. On my bike I have 30/39/50 up front, and I don't think I could go smaller than 30 without moving down to a 48T big ring. But the OP may find his FD can handle this just fine. Usually the manufacturer's specs would list the FD capacity.
It's been my experience having done more then a few 30T to 26T (+ or -) granny exchanges that the shifting can be quite fine. But this is where the rider can contribute a lot to the results. In that their technique far outweighs any ft der aspects. If the rider knows how to and actually does shift with "soft pedaling" technique the resulting expansion of range (the smaller ring) is no big deal. If the rider jam shifts then even within the stated range the results are poor shifting response. This is a case where the rider has a lot of control as to how their experiences will go. Andy