I have a 20" folding bike that is about a month old and came with a Tiagra drivetrain. I subsequently switched it out to a 11 speed drivetrain (Shimano 105 R7000 with flatbar SL-RS700 shifter). The cassette is an ultegra 11-30t and the chain is a KMC X11EL. 56T single chainring in front. all are brand new.
I was having indexing issues in that when I tuned the tension just right for the smaller cogs, the bigger cogs would have its indexing slightly off such that it will chatter. I would then have to turn the barrel adjuster clockwise, but when I went down to the smaller cogs, I would then experience a bit of chain chatter.
Having Googled extensively I thought the issue would be either the cable or the hanger. So I changed the shift cable and housing and made it slightly longer than needed to avoid shifting issues due to kinks etc. Then I bought the park tools dag3 and aligned the hanger to about a 1mm-2mm tolerance (think it was off by about 4-5mm at the start).
Changing the cables and housing didn't change a thing, though aligning the hanger seemed to help somewhat. However, I am still experiencing the symptoms (in that when I index for the smaller cogs, I need to make the cable tension looser by about two or three clicks when I move to the larger cogs for it to be perfectly indexed) though I am able to find exactly one or two barrel adjuster positions that works reasonably well.
However, I notice that, when shifting from smallest to largest cogs, everything seems ok. But when shifting from the largest to second to third largest cogs, I get the same chatter noise and I need to turn the barrel adjuster about two clicks clockwise. But if I do so, I get a very slight chain chatter on the 2nd and 3rd smallest cogs. I tried changing shifter cables again to another Shimano but this did not help. The sound is very subtle but noticeable. I confirmed this by recording a slow motion video on my phone and the chain rubs against the smallest cog ever so slightly sometimes. Turning the barrel adjuster back anticlockwise works but then I end up with the same issue on the larger cogs.
Now the kicker is... I feel this only on the bike stand but when riding, I don't notice it at all. I brought it to a reputable LBS near my house and they mentioned that my drivetrain was perfectly smooth (though granted the shop is a little noisy so I was unable to reproduce the very slight chain chatter on the smaller cogs).
I also noticed on the park tools video on rear derailleur adjustment, the guy also needed to turn the barrel adjuster clockwise a little to get the larger cogs to stop chattering, but when he moved back to the smaller cogs, if you hear carefully there is actually a little bit of chain chattering against the next cog, though he claims in the video that it is indexed properly.
So... Could my expectations just be too high? I've already tried 2 different cassettes, shifters and RD, even put on a new hanger and realigned so I'm really not sure what else could be wrong (kmc cables being too thick, perhaps?). Also played with b tension which didn't really help much.
I'm wondering if it's normal for the upshifts to be very slightly different from the downshifts? And is it normal for indexing to be very slightly off in different cogs?