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New FD/RD: chain alignment issue?

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New FD/RD: chain alignment issue?

Old 03-21-20, 10:23 PM
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New FD/RD: chain alignment issue?

I just installed an Ultegra R8000 FD and RD -- moved from short-cage 6800 RD to another short-cage. No change in cranks, cassette, or chain length. Painstakingly got them dialed-in where they are shifting relatively well, but for some odd reason, when I go small ring (36) to the 11, the chain catches on the ramps of the back of the big chainring and tries to pick it up. It does it a little bit in the 12, as well. The FD cage is nowhere near touching the chain on either side, so it's not the culprit.

I have the high limit screw on the rear set perfectly to where it'll just barely shift into the 11, so unless there is something I'm not taking into account, it's also not the RD positioned too far over toward the frame and increasing the crosschain angle.

I know I'll get responses of "well you shouldn't ride little-little anyway," and I get that, but it's not the point....at least once it's going to inadvertently happen and I don't want the chain getting yanked into the derailleur cage under power at 30 mph.

Tips? Suggestions?
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Old 03-22-20, 12:01 AM
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Must have been happening with the old FD and RD and you just never noticed it. What you are describing is not caused by either derailleur. The derailleurs just move the chain onto a set cog or chain ring, and then do nothing more until you move them. Rather the path the chain takes from the top of the small cog (or 2) to the top of the small chain ring just happens to pass through the arc of the large chain ring, and thus gets caught on the teeth of said large chain ring. So I wont say don''t cross chain, I will just say get a smaller large chain ring that doesn't interfere with the chain passing from the smallest cog to the small chain ring,
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Old 03-22-20, 01:40 AM
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You old FD was rubbing a tiny bit, just enough to keep the chain off the ramps of the bigger chainring.
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Old 03-22-20, 05:50 AM
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It's completely normal for the chain to catch on the shift ramps of the large chainring in that situation, especially on bikes with short chainstays.
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Old 03-22-20, 06:30 AM
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If you have sufficient derailleur throw you can use thin (I think 0.4-0,6mm is the thinnest) chain ring spacers to move the big ring outboard a bit. I needed to do this when I replaced the big ring on my 22-32-42 with a 46 ring; worked fine. But you should still avoid small-small. As stated, if the chain is not touching the derailleurs they have nothing to do with this.
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