Unusual resistance fluctuations on incline/decline changes

Bugs and Support
1

Hey everyone, I’ve got a tough one that I just can’t figure out.

I’ve been happily riding my Wahoo Kickr Core on Zwift for years, but over the last few months my trainer has been randomly spiking its resistance. Some observations:

(1) While peddling ~180 watts in free ride mode, when I encounter an inline or decline, my power will spike for a split second either up or down—as high as 300w.

(2) This only seems to happen on elevation changes—not at any other time.

(3) What it feels like is Zwift sending the wrong gradient change to the trainer—e.g. downhills feel like they have more resistance than they should, and uphills less. It’s especially noticeable on rolling hills. Besides the power readings, the trainer simply feels all out of wack.

(4) ERG mode on Zwift works perfectly

(5) Setting trainer difficulty to zero also resolves the issue.

I suspect there’s some kind of bluetooth issue, but I can’t for the life of me figure it out. I’ve tried:

(1) the unusual unpair/restart/pair dance
(2) turning off all other devices that could connect to the trainer, including my iPhone and the Wahoo App
(3) reinstalling Zwift
(4) trying Zwift on another laptop. Everything went back to normal for one ride, but then starting acting up again immediately

I also submitted a support ticket to Wahoo. We confirmed the trainer is in fine shape with an ERG test. It’s on the latest firmware—v1.5.36.

Anecodally, this started happening around the time when I downloaded the firmware upgrade for auto-calibration.

Any ideas? Very frustrated since I can’t race with my trainer like this.

Screenshot 2025-01-24 at 10.15.30 AM
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2

There’s a chance this is related to the issue that Zwift are investigating in the following thread:

3

I’ve had exactly the same issue for a number of months. I did the tests with Wahoo and they said it was Zwift. I didn’t get the same experience when free riding on Rouvy. I have had a knee injury recently so haven’t been riding much to continue diagnosis, but confirm that knocking the trainer difficulty down to 0 also meant the issue went away for me. It is back now that I have knocked it up slightly.

4

Glad to hear I’m not alone.

Posting a screenshot from today’s ride. I was on Tempus Fugit—easy to hold zone 2 with only 1 or 2% gradient changes. You can see how the resistance spikes for a split second and my power moves up to yellow/red.

Zwift 1.85.0 (141681)
MacOS 12.7.6
Wahoo firmware v1.5.36

I’ll try opening a ticket with Zwift support.

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5

I got to the stage with Zwift support where they think that it is bluetooth / wifi interference. I’m not convinced because I’m using the same set up and same location I have been using for years. I was going to move my equipment to show it still occurs elsewhere to take that out of the equation.

6

I did exactly that last month—different room, different laptop, same trainer. Same effect. Can’t figure it out.

Is there a way to see what commands Zwift is sending the trainer? e.g. resistance adjustments?

7

I’m not sure.

I’ve done a ride and downloaded the Zwift log file and fed it into Zwiftalizer.com. The report showed no bluetooth or networking issues for the whole ride.

However I experienced the same micro resistance drops and spikes. It’s mainly when there are changes in gradient. I was riding the Flat Route in Watopia and ot was prominent every time I climbed up from the bridge after the sprint and all along the undulations and the drop down into downtown - on every lap. On the flatter sections of the route no issues.

1 Like
8

Oh brother—100% the same. I also checked with Zwiftalizer and couldn’t find any issues.

I have a ticket open with Zwift. I’ll keep this thread updated.

Makes it slightly better that I’m not the only one with this weird bug.

9

An update. Having had Zwiftalizer show no errors and Zwift support confirming that was the case, I contacted Wahoo to ask of they could suggest more diagnostic tests. They came back to me saying they were going to issue a refurbished replacement because my turbo is out of warranty (I had to provide a copy of receipt and serial number). I’m now working through that process.

1 Like
10

Great to hear! I ordered an ANT+ dongle to rule out bluetooth, and sure enough it’s still happening. Hopefully Wahoo Support will be equally helpful here. :slight_smile: