Virtual shifting prevents autocalibration on KICKR Core?

I am definitely experiencing the same issue described by some of the folks here.

  • Kickr Core (1.5.5) via BLE FTMS + Garmin CAD sensor via ANT+ (cadence reported by Kickr is too choppy because I’m a novice cyclist and my pedaling smoothness is nonexistent).
  • Happens only in SIM mode with Virtual Shifting ON – ERG mode is buttery-smooth.
  • Happens in any RPM, but most noticeable in low RPM “uphill”, and the lower the virtual gear the worse it gets – 60rpm in vGear 2 on a +7 grade feels like alternating between stomping and spinning out every few revolutions while the PWR display dances between 30 and 200W!
  • Real gearing is 24t front, 21t rear – I use a 2x8 MTB as my trainer bike. Zwift Cog that came with the trainer did not align out of the box and did not work with the provided 8spd shim, so I had to improvise and purchase a secondary 8spd cassette for trainer use.
  • No IRL shifting, that’s what virtual gears are for, right?..

Here is how a 10min flat-ish portion of a ride looks like, believe me, inclines are even worse. The fluctuations are not display-only, I can feel this constant power wobble through the pedals and it’s incredibly annoying:

I noticed there were at least a couple other reports of this issue under Bugs that went unanswered:
spiky-power-with-consistent-cadence/631744
kickr-core-virtual-shifter-bug/629376
pulsating-resistance/619048

P.S. The Start Chat button on the Contact Us page doesn’t seem to work, so I can’t even start a support case on this. :roll_eyes:

I’ve been paying closer attention to pacer rides. Typically a rider increases and decreases power to maintain a certain position in the pack, and because of dynamics/ churn, sometimes that needs to be a strong surge or a substantial reduction in power. What I’ve noticed is that when using manual shifting, the surge with any given cog is much more responsive and immediate compared with doing the same in any given virtual gear. So over the course of a ride, the additional (“unrecorded”) effort with virtual shifting seems to be much more than manual shifting. After an hour or so, the average reported power for the same pacer is very close, but the perceived effort is massively different.

Am I imagining this??!!

You answered yourself. Your front sprocket is too small. Sufficient flywheel speed is required for stable operation. Your problem is getting worse, that’s understandable. The slower the flywheel rotates, the more power the trainer needs to hold it. The faster it spins, the easier it is to maintain power stability.

  • Happens in any RPM, but most noticeable in low RPM “uphill”, and the lower the virtual gear the worse it gets – 60rpm in vGear 2 on a +7 grade feels like alternating between stomping and spinning out every few revolutions while the PWR display dances between 30 and 200W!

Thanks, that sounds logical - I will try my large sprocket combo, which will be 36f/16r but it is much noisier than having the chain mid-cassette with the small sprocket in the front.

My point, however, was that I’m only experiencing this drastic power wobble in virtual shifting – I never had any issues with pedal feel when using conventional shifting, even when climbing a 9% grade (100% trainer difficulty) in the granny gear (24 front - 40 rear)!