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Putting 11-34t cassette on CX Bike

k1banjok1banjo Posts: 6
edited May 2018 in Cyclocross
My son-in-law recently bought an used Cannondale CX bike with Ultegra Rear Derailleur, 11-28t cassette and FSA 50-34 Crank. We live in an area with some pretty steep long gravel climbs and he would like to make it more climbing friendly. I called Shimano and they informed me that the biggest cassette that we could put on with a long cage rear derailleur is a 11-30t. Does anyone have any experience or suggestions? Thank you for your help.

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  • milemuncher1milemuncher1 Posts: 1,472
    k1banjo wrote:
    My son-in-law recently bought an used Cannondale CX bike with Ultegra Rear Derailleur, 11-28t cassette and FSA 50-34 Crank. We live in an area with some pretty steep long gravel climbs and he would like to make it more climbing friendly. I called Shimano and they informed me that the biggest cassette that we could put on with a long cage rear derailleur is a 11-30t. Does anyone have any experience or suggestions? Thank you for your help.

    A long cage Shimano RD will take a 34 t big sprocket, with a 50t chainring, no worries. The medium cage would be pushing your luck, but a long cage will take it.
  • oxomanoxoman Posts: 9,270
    I currently run 48/34 with a 11/32 with no issues and will probably go bigger if I replace rear cassette and possibly single speed.
    Too many bikes according to Mrs O.
  • green_markgreen_mark Posts: 74
    Check Youtube

    Loads of videos about with people using 5800 GS or 6800 GS RDs working with 50/34 x 11-36T

    34T should not be a problem.
  • timothywtimothyw Posts: 2,482
    You haven't really given us enough information.

    The key question is, how many gears does the cassette on the back have?

    If it is 10 (or less), then they are right, your existing derailleur is not compatible with 34 tooth cassettes - however, you can replace it with numerous other derailleurs to get 34t (or bigger) compatibility (for example the latest Sora GS is compatible).

    If it is 11, then it depends. If it's a 6800 ss (short cage) derailleur then officially it will only go up to 28 teeth at the back anyway, so you might already be pushing it.

    If it's a 6800 gs then officially the maximum is 32t, and as mentioned above, there's a fairly good chance you could use it with a 34 tooth cassette.

    The new r8000 gs ultegra derailleur is the only one that officially supports 34 tooth cassettes, but given you say the bike is used it seems very unlikely that you have one of those - if you wanted to be on the safe side then you should buy one of these along with the 11-34 cassette (assuming of course you are on an 11 speed system).
  • keef66keef66 Posts: 13,123
    If it's 10 speed Ultegra you can fit a 9 speed MTB rear mech and it will work with 10 speed road shifters and a 34t cassette. Quite a common thing on touring bikes.
  • k1banjok1banjo Posts: 6
    Thanks to everyone for the info...all very helpful. BTW, its a 10speed. Thanks again, Bob
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