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I have recently changed my cassette from a 11-32 to a 11-25 (11 speed). To make the change possible, I have reduced my chain size to 106 links (53 inches) by the largest cog, largest chain ring method. For further information, my crankset is a 52-36 teeth.

When I installed my RD-6800 (SS), I noticed that even by removing the B-screw, the derailleur is never too close to the largest sprocket (largest sprocket, smallest chain ring configuration). How is that possible?

I thought that maybe I screwed up the chain sizing, but I have just recalculated using the equation and the recommended chain length is 53 inches:

L = 2*(16.125) + (52.0/4 + 25.0/4 + 1) = 52.5"

Is it maybe due to the bike or hanger design?

  • At the LBS I was told that shortening is not necessary in this case. 11-25 is inside the range of 11-32 and the derailleur takes up the tension. On the other hand, with a chain length adjusted for 11-25 it will be to short for an 11-32 cassette. – Carel Aug 8 '17 at 20:09
  • @Carel I wouldn't be shocked if without resizing the derailleur was too far away from the largest sprocket. But with the correct one, it is indeed bizarre. – gstorto Aug 8 '17 at 21:02
  • On your 11-32 cassette the 25 is the third sprocket. On the 11-25 it's the last. The RD will logically be in the same position if your chain runs on any of both 25s independently of the cassette. I have three rear wheels with 11-25, 11-28 and 11-32 that I use on an Ultegra GS-cage RD. The front is normally 52-36 but sometimes 50-34. All of those combinations run on a chain-length for 52/36 and 11-32 without trouble. With an SS-RD however 11-32 was over the limit of 11-28 and the chain was too long anyway for 11-25. In that regard a GS is more versatile. – Carel Aug 10 '17 at 7:20
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According to Shimano, the RD-6800 GS is designed for 28-32T largest cog, where the SS is designed for 23-28. http://bike.shimano.com/content/sac-bike/en/home/components11/road/ultegra1/rd-6800-gs.html http://bike.shimano.com/content/sac-bike/en/home/components11/road/ultegra1/rd-6800-ss.html They may have actually done something different to the body of the derailleur instead of just putting a longer cage on it. I don't know that for sure though. Of course, that doesn't mean the GS can't work with 25. Your chain length shouldn't affect the B position at all. It will only affect the rotation of the cage around the upper pulley.

  • Sorry, I incorrectly stated it was a GS. It is actually a SS. By pulling the chain, it gives me the impression the upper pulley would be closer to the largest cog if the tension was greater. – gstorto Aug 8 '17 at 21:47
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    If you shift into big/big combo, where is the pulley cage positioned? If there's room for you to take out a link in that combo, it shouldn't hurt anything to take it out. It's also possible, as you said that the hanger is just positioning the derailleur strangely. Photos would help diagnose. – Noah Sutherland Aug 8 '17 at 23:01

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