I have a Shimano 105 R7000 GS (medium cage) rear derailleur and would like to mount a 12-25 cassette. According to its specs, this should not be possible.
I am just wondering: why not? A GS-cage will manage a 25t sprocket fine in many cassette combinations and in reality go as low as 11t. I understand, there is a problem in the other direction and a max on how many teeth it can handle on the highest sprocket.
Would anyone know, why a GS derailleur cannot handle a 12-25 cassette?