Short vs. Medium Rear Derailleur Cage

jburbatt

So yesterday I swapped out my damaged rear derailleur for a new one, but realized while I was doing it that my tri bike has a short cage and I had bought the medium cage.  I installed it anyway, and it seems to be working fine, but since this is my first ever installation I was wondering if it will work in the long run (I seriously cannot handle another race where my derailleur goes haywire). 

I have a compact 50/34 in front, and a 12-27 in back.  The chain wrap capacity of the only 9speed derailleur I could find was 29 for the short and 37 for the medium.  I had thought that with my setup I'd require more than a 29 capacity [(50-43) + (27-12) = 31] which is why I went with the medium. 

So should I keep the medium cage or buy/install the short cage?

 

Norton

You'll be fine with the medium.