Swapping 6800 chainrings

[Exonerv]

I found 36t and 39t Ultegra 6800 inner chainrings on Amazon for <$19 each. It seemed cheap enough, so I ordered one of each. Currently I'm running a 50/34, but have never cared for the big drop to the 34 ring.

My questions:

Is anyone else running a 50/36 or a 50/39 combo in the 5800/6800/9000 rings? Any degradation in shifting from running the compact?

Can the inner chainrings be swapped out without dropping the crankset?

[11.4]

Yes, you can swap the inner chainring without removing the crankset. If you wanted to, removing the crankset is only two 5 mm allen bolts anyway.

As for shifting, if you look at your 34, it's right against the fattest part of the big ring. If you put a 39 on, it stands off a little farther from the inner side of the big ring. I've found it makes the shift changes without sucking, but some chains do have the tendency on a downshift to float with the inside drive plates on top of the small chainring teeth, rather than dropping down onto the small ring. You can tweak it a bit, but mostly if you hesitate in your downshift it wants to float there and you have to pop it back up and knock it back down harder. Hope that's clear. I have a 9000 42 ring that I use with both a 9000 and a 6800 50-tooth outer. Same kind of issue, but for some reason not as frequent as with the 39.

[Exonerv]

Very helpful info 11.4. Thanks for sharing your experience. I run a 39/50 on my 7800 group with no issues. Wonder if the problem you describe will also carry over to the 36/50 combo on the 6800 group?

[Cicli]

I run a 38/50 on my 6800. I havent noticed any issues. Well except that that useless 34 is gone.

[Exonerv]

Ha...I recalled you looking to dump the 34. I started to PM you when I found these chainrings on Amazon. Glad you found a good fit.

[11.4]

I don't think this would be a problem with 7800 because the big ring isn't hollow. The two rings are both basically flat plates and the spacing is the same regardless of which inner ring is mounted.

I have a 36 Praxis for 7950 that I tried with a 7950 50 when I was trying to debug the whole issue. I didn't see quite as much of an issue, but I couldn't say whether it was the ring or the 7950 vintage or just that there wasn't as much difference in diameter between the 34 and 36. I don't really think there's that much to offer between 34/50 and 36/50 since I really wouldn't use either one that much where I live now. I wanted to get a good 42/50 setup going and am still tuning that to see if it really works well enough. I can tell you that with 9070 Di2, it works just great, but the great thing about Di2 is that it does the shifting for you and makes any kind of chainring shift better.

[phutterman]

I run a 36t inner on a 6750 compact (because I prefer the 14t gap of a traditional but get more of the range I want out of the smaller rings) - so fairly similar hollow big ring - and do occasionally have the chain skate on the small ring rather than engage, but it's rare, and happens almost exclusively when I'm fairly far toward the top of the cassette (e.g., shifting at the beginning of a climb right after a descent) and smarter shifting largely prevents it.

I'd chalked it up to using an FSA inner that might not be spaced quite exactly the same, and wondered if a Shimano small ring (like the CX-70 branded 36t) would improve it, but it hasn't been a big enough issue to have sourced one to try yet.

[tylerbick]

I dumped my 6800 34 for a 39 also. I've had 0 issues. My boss did the same, although he's running Di2 (I'm mechanical) and had issues with the chain falling short of the full down shift (skating on top of the inner ring teeth). Am I silly to want a 51t outer ring?