Rear Dearilleur/Cassette Compatibility

Discussion in 'Bicycle Mechanics and Repairs' started by Bugner, 28 Apr 2010.

  1. Bugner

    Bugner New Member

    Location:
    Sarf London
    My head is spinning a bit I have been looking for ages at different derailleur cassette combos trying to work out what is compatible.

    Here is the situation, I currently have an Audax bike with SRAM road shifters with SRAM 50/34 compact and shimano (9 speed) 12-27 cassette.

    I want to stick with 50/34 compact, but want to install an 11-32 or 11/34 cassette to help with touring with loaded panniers.

    So I know I will need a new rear derailluer. I belive that the SRAM XX dreailluers are compatible with road shifters and that I would need a medium cage to cope with chain length/slack?

    So in a nutshell, before I purchase compenents is the following set up compatible??

    SRAM road shifters
    50/34 Compact
    SRAM X7 (medium cage) derailluer
    11-32 (9 speed) rear cassette

    Would I need to change front derailluer as well?

    TIA
     
  2. PpPete

    PpPete Guru

    Location:
    Chandler's Ford
    11-32 and 11-34 are supposed to need long cage (MTB) mechs

    Shimano road derailleurs will go a little further than the rated 27T
    My Ultegra medium cage mech / Sora shifters copes OK with 30T (and a triple front!)

    Someone on one thread recently claimed to have a medium cage road mech coping with a 11-32 cassette. I've not tried it - didn't read that until after I'd butchered some cassettes to build my 12-30

    I bet SRAM mechs will go further than the rated spec too.

    Try just changing the cassette and not the mech, see what happens?

    I can't see that you'd need to change the front mech.
     
  3. RecordAceFromNew

    RecordAceFromNew Swinging Member

    Location:
    West London
    If I were you I would do what porkypete suggested. SRAM long/medium/short rear mech official capacities are 43/37/30 respectively (capacity is sum of differences in front and back), and whether you need a new medium depends on what you already have.

    You will likely need a new, longer chain irrespective of whether you need a new rear mech, if you have not planned to get that already.
     
  4. Gerry Attrick

    Gerry Attrick Lincolnshire Mountain Rescue Consultant

    Your answer will be found here.
     
  5. Steve Austin

    Steve Austin The Marmalade Kid

    Location:
    Mlehworld
    Ime, medium length mechs work fine with 11-32 cassettes as long as you don't run cross gears ie big/big-small/small. You can't run enough chain for the system to work big/big AND small/small, so if you try running 'bad' gear combinations, you'll rip the mech off or break the chain.

    I've only ever used medium length mechs for about the last 20 years on MTBS with no problems. fwiw its always been with Shimano
     
  6. MartinC

    MartinC Über Member

    Location:
    Cheltenham
    What I'm not sure about is the compatibility between the SRAM road shifters and a SRAM MTB Mech. IIRC SRAM make 2 sorts of MTB mechs - Shimano shifter compatible ones and their own 1:1 actuation ratio ones which need a SRAM MTB shifter.

    I believe a SRAM road mech will cope with a SRAM 10 speed 11-28 cassette on a compact (50-34) drive train so the other guys suggestions are definitely worth a try.
     
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