Originally Posted by
Iride01
I've never considered a triple front so please educate me if wrong. However I don't see where the size of the middle matters to the front derailleur. As long as the DR cage can accommodate the chain drop from the large to small, I'd think there'd be no issue.
STI front derailleurs are designed for a particular size difference between the middle and big ring. If the middle ring is much bigger than the derailleur was designed for, the inner plate of the derailleur may contact the middle chainring. Moving the derailleur up can buy you some clearance on the middle chainring, but then the derailleur is positioned a bit high for the big ring, not to mention it reduces the capacity for a small ring.