Long or medium cage rear derailleur?


What is the difference in a med cage and long cage rear derailleur aside from the physical length? Where would you use the long as opposed to the med?

Thanks, Richard

Hey Richard.

No real difference other than the length of the cage. If you have three rings and a big cassette, you need a long cage to wrangle all that chain. To optimize shifting and minimize wayward chain syndrome (WCS), you want your chain as short as possible. You can roll a shorter chain if you’re rocking a single ring, a tighter cassette, and/or you really know how to shift.

I was just about to post this answer, then the obsessive compulsive part of me kicked in. So here we go:

Derailleur Capacity What that means
Long cage XT 45T With 22,32,44 rings and 11-34 cassette, you can use any gear combo. Idiot proof, but lots of chain slap.
Med cage XT 33T In the small ring you can’t go any smaller than the 23t cog. Which is fine, because by then you should shift to the middle ring. Slightly better shifting and less WCS.

I just installed a short cage SRAM X.9 on my Specialized SX. Short chain, clean shifting. Super tasty!

— Lee

5 replies
  1. MyEpic says:

    The 33T should say medium.

    To figure out the how many “T”s you need, take the difference between the big ring and small ring and add that to the difference big cog and small cog of your cassette. For most mtb bikes it is (44-22) + (34-11) = 45. That’s how many teeth the rear derailleur needs to take up if you cross the chain.

    If you follow the “rules” and don’t cross the chain (big ring, big cog or small ring, small cog) then a medium cage is good enough. But if you race (or are just lazy), you may want to cross the chain for short durations.

    The shorter the derailleur cage, the less flex, crisper shifting. But you have to be more disciplined in your shifting otherwise you will have too much slack when you are on the small ring or bind up your chain when you are on the big ring.

    If you go for medium, keep track of the gear indicator on you handle bars.

  2. josh says:

    hey up, was just reading this cause a friend of mine has an x.9 short cage going cheap, i am using one 36-tooth wheel on the front and a 11-32 8-speed casset on the back, will the short cage be compatable with this setup, cheers

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