Rear derailleur question

devhads
devhads Posts: 236
edited April 2014 in Workshop
I'm going to set my cross bike up 1x11 with hopefully an 11-32t cassette and a 42t narrow/wide Race Face chainring. The Ultegra rear mechs lists 30 teeth cogs maximum but am I right in thinking that's with a double. For example would the chain wrap capacity for my set up be (42t-42t) + (32t-11t) = 21t meaning I could get away with a short cage mech?

Does the 'bearing equipt tension pulley' mean I can alter the tension of the spring to help keep my chain with the single chainring. I'm not planning on using a chainguard.

Comments

  • Monty Dog
    Monty Dog Posts: 20,614
    The mech capacity is fine, but it's down to the distance between the top jockey wheel and the big sprocket and often depends to the dimensions of the rear mech hanger - I'm afraid the answer is try it and see if it works.
    Make mine an Italian, with Campagnolo on the side..
  • paul_onabike
    paul_onabike Posts: 194
    I don't think the Ultegra rear mech can deal with a 32 rear sprocket.

    I can see what your thinking is with the single ring setup but I don't think it will work in practice. I would expect that your chain will be constantly coming off. You will need a chain guard.

    Another problem with using wide ratio cassettes is that there are big steps in gear ratios, and you can guarantee the ideal gear will be in-between what you have. The most useful setups use a close a ratio cassette and a double compact front.

    When descending on the 11 there will not be enough tension on the chain to keep it on the front chain-ring, especially if it's bumpy. Also don't forget that you will also have to stop to put the chain on.

    You can't alter chain tension with the spring. The tension pulley is just the lower jockey wheel.
  • Monty Dog
    Monty Dog Posts: 20,614
    Previous poster obviously doesn't know about narrow/wide chainrings so ignore comments re chain guard - lots of people run single ring for CX. The spec for the 6800 GS mech says it'll work with a 32 sprocket - the short cage 'might'
    Make mine an Italian, with Campagnolo on the side..
  • rafletcher
    rafletcher Posts: 1,235
    Monty Dog wrote:
    Previous poster obviously doesn't know about narrow/wide chainrings so ignore comments re chain guard - lots of people run single ring for CX. The spec for the 6800 GS mech says it'll work with a 32 sprocket - the short cage 'might'

    I always thought both SS and GS 11sp worked with 30T, the GS has greater overall capacity for a triple chainset, the SS will only do doubles.

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