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Right derailleur for a 12-30T

Picked up my new (second hand) bike last week. It was such a bargain, that when I collected it, I failed to ask what the gearing mech ratios were. After struggling to climb on my first ride, it became apparent I didn't have 'much at the back'. It's Shimano Ultegra 6700 (Di2), 50/34 at the front; 11-25 at the back. So, I need help...
The 12-30T looks like the best option to help me lump up climbs. However, I suspect I'll need a medium cage derailleur and possible a new, bigger chain?
Would this be the case? Or can I just get away with a new cassette?
Thanks in advance,
Kevin
Trek 2.3 2010

Posts

  • dj58dj58 Posts: 2,086
    edited 6 June
    There is only one Model DI2 RD-6770-SS and the maximum low sprocket is 28T, according to the Shimano DM. Although the chain length section on page 23 refers to "*If the largest sprocket is 28T or more" so maybe a 30T will work! I have no experience of 6770 only 6700 mechanical so cannot tell you if the CS-6700 12-30T would definitely work, the CS-HG500-10 12-28T will.
    https://si.shimano.com/pdfs/dm/DM-0001A-006-ENG.pdf
  • es330es330 Posts: 46
    Thanks, you’re right. I’ll have to settle on a 28 :( but get fitter!
    Do you know if I would need to get a longer chain?
    Trek 2.3 2010
  • dj58dj58 Posts: 2,086
    edited 7 June
    Yes at least two links longer to be on the safe side, refer to the chain length section of that Shimano Dealer Manal I linked to. Do some internet searching on the RD-6770 to see if it could work with a 12-30T. Buy a new chain with a quick link.
    Edit
    This post seems to suggest that a 12-30T cassette will work with the appropriate length chain and adjustment of the B-Tension screw
    https://forums.roadbikereview.com/components-wrenching/cassette-size-di2-10-speed-346315.html
  • ugo.santaluciaugo.santalucia Posts: 24,367
    ANY 9 speed (yes, I said 9 speed) Shimano mountain bike derailleur will work: XT, LX, Alivio etc... 10 speed ones won't work. I have the same setup
  • webboowebboo Posts: 2,154
    Are sure a 9 speed mountain bike rear mech will work with Di2
  • ugo.santaluciaugo.santalucia Posts: 24,367
    webboo said:

    Are sure a 9 speed mountain bike rear mech will work with Di2

    Di2? I didn't read properly, I thought he mentioned 6700, didn't know it also came as Di2
  • amrushtonamrushton Posts: 658
    No mention of Di2 in the original post
  • ugo.santaluciaugo.santalucia Posts: 24,367
    amrushton said:

    No mention of Di2 in the original post

    AH, thanks... I though so
  • webboowebboo Posts: 2,154
    amrushton said:

    No mention of Di2 in the original post

    So Shimano Ultegra 6700( Di2) 50/34 is not mentioning Di2.
  • Current and previous series short cage non di2 will take up to 30t and can’t see the arm length being any shorter on 6700 di2. Worth giving a go in my opinion.
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