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I'm considering changing my 10 spd Shimano 105 cassette to an 11 spd Ultegra cassette. Do I have to change the rear derailleur or can I use the existing derailleur? Can the existing derailleur be adjusted and shift to the additional cog? Are derailleurs "speed" specific - 10 spd derailleurs, 11 spd derailleurs? Same for chains? Are they different for different size cassettes?

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  • Do you have a 11 speed shifter in the first place? Why do you are you looking at a 11 speed cassette if you have a 10 speed drivetrain at the moment?
    – Batman
    Mar 25 '17 at 15:01
  • Generally the rear derailleur mech doesn't care about number of gears because the indexing is in the shifter. The rear mech has to clear the largest gear with the upper jockey wheel, and also have enough left/right movement. You need a replacement right-hand 11 speed shifter though, and probably a new chain. I see no clear gains by doing this change.
    – Criggie
    Mar 25 '17 at 20:31
  • Thank you all for the answers. Yes I can see the perplexed looks on your faces... why make the change? Batman, more to have the same components (Ultegra) on the bike, performance is fine. And if I was going to change the cassette I thought I go with 11 spd. Criggie, from discussions w/ experienced riders I knew I have to change the R shifter, but conflicting stories on the derailleur. No one mentioned the chain! Thank you all.
    – Mario R
    Mar 26 '17 at 14:49