I currently have an Ultegra RD6500 9 speed rear derailleur. I have a 30/42/52 triple and my cassette is a 12-26. My bike came stock with 106 links in the chain. My rear derailleur is marked with RD6500 with no SS or GS following the number to distinguish between short and long/medium cage. I need a new derailleur and I can only find RD6500 or RD6700 derailleurs listed as short cage. I read that the medium cage is required because I have a triple. But I also read that a short cage can handle a rear cassette up to 27 regardless of the front. The question is --- can I use a RD6500 or RD6700 short cage on my setup? Kindly - Don

Calculate the total capacity required. This is the sum of the tooth differences between your large and small chainrings AND your largest and smallest rear cogs.

So....

Capacity = (52 - 30) + (26 - 12) = 36

Shimano has increased the total capacity in recent years. The 6500 series had capacities of 29T (SS) and 37T (SGS). The 6700 series bumped that up to 33T and 39T, respectively.

A mid-cage would be the correct match for your drivetrain. Some people have spoken of running an SS in your situation, with the requirement of staying out of all but the few largest cogs while in the small ring (to circumvent the short cage's inability to take up the excess slack).