Originally Posted by
cderalow
....you might be able to get a mountain type front derailleur to work with 105 shifters... not sure 100%.
that would allow you to get down to the 24T granny inner.
No need for an MTB front derailleur and it won't work with road STI's, particularly on a triple. The standard 105 front derailleur is correct for the big chainring's curvature (50T on current FC-5703 cranks) and will easily handle a 24 or 26T replacement granny ring. I have two FC-5703 cranks on my bikes and the 26T granny works fine. As noted, the shift from the granny to the middle is a bit sluggish but you will almost never be in a hurry for that one.