Originally Posted by
dr_lha
I haven't done the tooth calculations, but I'm damn sure that with a compact up front and a max 30T at the back, you can get away with the short cage. This is certainly true of my RD-5701 105 rear derailleur. Pretty sure you only need the medium cage if you're running a triple or want to go up to 32T max.
I agree that it would work.
However, if you rear the OP's other thread on this issue, where he took umbrage at someone's statement that it will work "fine," you will understand that he does not want a setup that he can "get away with."
Yes, you should never cross chain, which is the only scenario that would require the full capacity, but from
a strict specifications point, the short cage is rated for 31T; his setup is 34t.
This derailleur was replaced by a LBS; they should have replaced his broken derailleur with a like unit.