Overall capacity and max sprocket size
I have a yr 2000 Peugeot Pulse. It has 39-52 double chainring and a13-24 x8 speed shimano cassette and short cage derailleur. Need a bit more flexibility. From what I can see, the short cage has a max capacity of 29 and a max sprocket size of 27, so either the 12-25 or 13-26 should fit. But I also note that there are Acera cassettes with wider ranges 11-30,32 or 34 - but I presume I would have to fit a longer cage to accomodate any of these? ( and there is different info out there on whether the max sprocket size for medium cage is 27 or 34 - any advice?).
Last alternaitve would be to fit a triple up front (shifters labelled 'Sora Triple' even though it is only a double), but would I need new cranks etc to do this? Any advice welcome