Derailleur Question: Replace RD-6870-SS with RD-8050-GS?
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  1. #1
    RoadBikeReview Member
    Join Date
    Apr 2008

    Derailleur Question: Replace RD-6870-SS with RD-8050-GS?

    I'm getting older with injuries and want to put on the Shimano 11-34 cassette, CS-HG800. I have the 2014 Ultegra Di2, short cage. I know my RD-6870-SS will not work so I'm thinking of getting a RD-8050-GS. I know that will require a firmware update.

    1. Will the direct mount be a problem or does the bracket already on the RD-8050 fit my current derailleur hanger?
    2. Will my current electric cable just plug into the RD-8050?
    3. Will my junction box, SM-EW67A, be compatible with the RD-8050 with the firmware update?
    4. If not, and I can find a new RD-6870-GS, can I just replace the derailleur without the firmware update? I know to adjust the B-Screw, etc.

  2. #2
    Adorable Furry Hombre
    Reputation: Marc's Avatar
    Join Date
    Jan 2005
    #1 Fit will not be an issue. Use the included and pre-installed B-Link

    #2 All your parts are e-tube. Yes. Plug and play. Use an e-tube connector tool for unplug and re-plug.

    #3 Per the latest Shimano compatibility chart, if you are using the BTR2/BMR2 then yes:

    #4 You would probably need to do a firmware update anyway. Di2 parts have an astounding variance in what firmware they ship with even from the same retailer.
    "Refreshingly Unconcerned With The Vulgar Exigencies Of Veracity "

  3. #3
    RoadBikeReview Member
    Reputation: Srode's Avatar
    Join Date
    Aug 2012
    Works fine, I did the same to use a bigger cassette but in my case an 11/36, I was able to use 11/34 with the 6870 long cage.

    If you have the new battery (BT-DN110) you will have 'Gear Control' with the new set up, and in fact might have it with the older battery too, I haven't tried it. Gear control prevents cross chaining small small to the first 2 cogs on your cassette which helps keep you out of slack chain situations.
    Gravel Rocks

    Trek Domane
    Niner RLT9 (Gravel Bike)
    BH G7 Disc
    Trek Crockett

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