i'm currently running 12-25 in the rear with 53/39 in front. my question is... if i were to change the rear to 12-27 (for climbing hills) then will i have to adjust anything on the rear derail.?
also, is there a big difference between 12-25 vs. 12-27 in climbing? i know that the only difference between them is the last 3 largest cogs, so can i just purchase that part only instead of the whole cassette? if so, where can i buy it from?