Just got a Wahoo Kickr v6 + Zwift Cog (“Wahoo KICKR with Zwift Cog and Click”) and thought I’d try virtual shifting. However, I get ~3 second power oscillations. Happens with or without race mode enabled, and only when virtual shifting is enabled. Example from a race:
After some research, turns out Wahoo has gear ratio requirements for virtual shifting to work. My chainring is 48-32, and the Zwift Cog is 14-tooth. So, because I was in the little ring my gear ratio was 2.29 which is less than the “2.5:1 - 3:1” recommended range (see Wahoo Support, “Zwift virtual shifting with Wahoo smart trainers”).
Could this explain these power oscillations? Update: shifted into the big ring (48-tooth), but issue remains!
Zwift v1.105.3, running on ASUS ROG Zephyrus G15, Windows 11 Home, 16 GB RAM, etc.
Wahoo KICKR 84DD Firmware v5.4.29, connected via Wi-Fi.
Other connections: KICKR Climb, Click v2, and sometimes a TRACKR HR monitor.
Yes that is the usual symptom when the physical gear is too small. 34x14 is their recommended minimum, and even being right at the minimum sometimes causes problems. Either use the big ring, or get a 3rd party cog smaller than 14 teeth.
I just got a Kickr Move and experienced the same yesterday. I have a cassette on the back instead of the cog. The oscillations disappeared when I shifted one cog down the cassette, so I also assume your problem is the «gear ratio»-issue.
Your setup seems to unfortunately reside in no-mans land. You can’t get to the recommended ratio using the default 14t Cog. You could in theory swap in the 18t Cog ring that is supposedly available, and then use the 48t front ring. IMO the Zwift Shop is a bit negligent in only asking you what Brand and Trainer you have when you order a cog, instead of asking you what your chainring configuration looks like.
Wahoo Support documentation says it should be “at least a 2.5:1 - 3:1 gear ratio”, which I had interpreted to mean above that approximate range, not within that range. Time to reach out to Wahoo themselves for clarification!
I confirmed with Wahoo that, as you suspected, they actually mean a gear ratio between 2.5:1 and 3:1 is required for Zwift virtual shifting to work properly. They’re going to update their documentation at some point. I also did some tests to confirm that this is the case:
In summary, the default Zwift Cog (14-teeth) will not work with Wahoo trainers if you have 48-32 chainrings because you cannot achieve a gear ratio between 2.5:1 and 3:1!
