How to properly adjust rear derailleur for Wahoo Kickr?

Question

I have a Merida Escultura 100 connected to a Wahoo Kickr (with the rear wheel removed, of course). I've ridden this combination for over a year and had the derailleur adjusted more or less so there wasn't a lot of chain chatter, although sometimes the chain would to the next (rear) gear from the selected one (that is, it would pop off the selected gear to the next one), so I sometimes had to do some adjustments of the tension.

In any case I had to take the Merida to the shop a couple of days ago because, among other things, the cable to the rear derailleur broke. They said the limits for the rear derailleur were way off. Now I've gotten the bike back and they've adjusted it to the Merida's rear chain set. But now when I ride it connected to my Kickr, however, I get a lot of chain chatter when the rear gears are either at their lowest or highest, particularly (of course) when the front gears are high and rear low (crosschaining?), and vice versa. But not only then: whenever I'm in the lowest or highest rear gear I get a lot of noise. And I believe - although a bit hard to tell - that the chain is rubbing the chain guard (see first photo below).

Obviously I need to adjust the derailleur. How can I get the chain to stop rubbing the chain guard, if it's doing so, and stop making so much noise at the extremes? I attach a photo of the adjustment screws, below. I know one is lower extreme, one is top extreme, but I don't remember what the third is for. And could you remind me which way should I turn each of them in order to get the chain to stop rubbing the guard at the extremes? I attach a second photo, with each screw numbered. Something like "turn screw 2 counter-clockwise to stop chain hitting at low extreme" (if that's the case), would be very helpful.

Thanks for any info!

Answer 1

OVERVIEW: To identify your components, your numbers are:

1. "B" screw, or body-angle screw = usually does NOT need to be adjusted (more on this below*). This adjusts your derailleur's angle to the rear cassette gears.
2. and 3) Your Lo- and Hi- OR Hi- and Lo- Limit screws = which is which depends on YOUR bike. Some (not all) are labeled H or L. These LIMIT your derailleur's inward and outward movement, so the chain does NOT choke between cassette and: A) Spokes, or B) Frame (outer).
3. Below your 3) is a 4th component, the Barrel adjuster, with 3 of 4 visible raised-bump finger grips. Look for an identical component near your shifter. The Barrel adjuster fine-tunes your cabling vs derailleur spring tension AFTER proper INDEXING has been set (> 1. Park Tool Rear Derailleur).

DIRECTIONS: To answer your adjustment question, I'd like to start with sharing there's really good resources out there; I'll share two here:

.1. Park Tool Videos on YouTube = EXCEPTIONALLY good mechanical and conceptual teaching on all things bike-related; the intuitiveness of these videos is outstanding for layman and tech alike. Here's the fairly brief Rear Derailleur video ... Rear Derailleur - Indexing & Limit Screws

... and more on Adjusting, if you prefer a blog *-AND, it has an excellent write-up on the "B" (body-angle) screw. Rear Derailleur - Adjustment ...

https://www.parktool.com/en-us/blog/repair-help/rear-derailleur-adjustment

(Interestingly, this PT blog from 2015 instructs in a different order than the video).

... and here's Park Tool's main channel ... Park Tool How-To Repairs-YouTube

https://youtube.com/c/parktool

.2. This Wahoo forum page ...

https://wahoox.forum.wahoofitness.com/t/how-to-avoid-rear-derailleur-adjustment-on-kickr/14588/14

... has plenty of great ideas, including: a) Get two identical cassettes. (They did not elaborate, but I'm assuming two Wahoo cassettes). b) Get a heavier steel frame bike to devote to indoor training (I do this too). c) Learn (= what you're already asking) about how to adjust your rear derailleur with each wheel swap (see Park Tool above). Various responders had different scenarios, each requiring a different adjustment.

.3. To recap #1, Park Tool video contents to INDEX the Rear Derailleur: mm:ss 00:00 Premilinary Info; 00:48 Derailleur Adjustment; 03:06 L-Limit Screw Adjustment; 05:58 H-Limit Screw Adjustment; 09:40 Indexing Adjustment.

Final note: You'll notice I did not tell you to "turn screw 2 one turn counterclockwise" or similar, as for one I don't know your initial settings, nor whether anything's been changed since your LBS visit.

Learning the Park Tool videos will empower you to understand and DO all of this very well, as it has done for me.