Chain length for short cage mech
I want to (possibly temporarily) use a short cage rear mech on a set up that should ideally have a medium cage. Front chainrings are 50/34 and rear sprockets are 11-34. I wont be bothering the biggest 3 or 4 sprockets in the big ring so happy to use the short cage mech that is on the bike at the moment if I can. My question is, what is the best way to calculate chain length for this? Should I take for instance the 26 tooth sprocket as my largest and measure chain length using that or would I just be better using my largest 34 sprocket for the measurement as normal.