Short or medium cage mech?

homers_double
homers_double Posts: 8,279
edited March 2015 in Road buying advice
I'm upgrading my Allez with a few 105 bits and have come to the rear mech, I'm running a 52/39 compact with an 12/30 cassette so do I need a short cage mech?

I'm thinking the medium cage would be for a tripple clanger up front?
Advocate of disc brakes.

Comments

  • arlowood
    arlowood Posts: 2,561
    I have run short cage RD's on all my recent bike builds with a 12-30 cassette and compact 50/34 chainset.

    You should be OK with a 52/39 tho' there might be a slight question mark over the capacity if you plan to run big/big (52/30)

    Just make sure you get the correct chain length when setting up.
  • keezx
    keezx Posts: 1,322
    homers double wrote:
    I'm upgrading my Allez with a few 105 bits and have come to the rear mech, I'm running a 52/39 compact with an 12/30 cassette so do I need a short cage mech?

    What's compact about 52/39?
  • homers_double
    homers_double Posts: 8,279
    Nothing, thats a mistake on my part as CRC don't have the compact in stock so I'll be shopping elsewhere...

    But going back to compact sizes I think I'll go for the short after doing a bit of digging.
    Advocate of disc brakes.
  • iron-clover
    iron-clover Posts: 737
    For that set up a short cage will be fine- it has max 16t difference for the front (the same as on a compact- your standard only has 13t difference) and a 34t difference overall.
    Your rear cassette has an 18t difference so on that set up you have 13t difference for front, and 31t total difference, which is well within the range of the mech.

    That cassette would be the limit if using a compact though, and you can't use a bigger sprocket than 30t with the short cage.
  • darkhairedlord
    darkhairedlord Posts: 7,180
    if you are fitting 10 speed 105 the RD is 33T capacity.

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