When I use Zwift in workout mode, I might have, say, a 5 minute interval @ 250w (keeping this simple for illustrative purposes). I set the turbo trainer firmware to “power smoothing/average”. I set Zwift to “3sec power average”. I enable ERG mode in Zwift. I start the workout.
My expectation when I hit the 5minute interval is that effectively I’m making a “bargain” with the trainer - I will keep pedalling and it will give me the correct resistance to keep me at 250w. That isn’t happening (consistently). What actually happens is that the trainer holds a relatively constant resistance (sometimes for up to 5-10 minutes) but then, for no reason that I can fathom, the resistance drops very significantly for one second (two max) before resuming.
When this happens the reported power (both as shown on screen in Zwift and as reported in the fit file data) dips. The odd thing is that it dips to around 66% (2/3) of the value it should be holding. This amount does vary slightly sometimes/there are exceptions but say 90% of the time it dips consistently by the same amount. So if holding 250w, it drops to 160-180w briefly. Less than a second and the normal reported power and resistance resumes.
This is intermittent and happens throughout a ride. I have noticed that it seems to happen more frequently the longer that I ride. So it could potentially be due to the Kickr “overheating” in some way (though its very cold here currently and the room I ride in is extremely well ventilated and this is still occurring).
However my suspicion is that its something about my “pedal dynamics”, cadence or bike position and my pedal motion changing or cadence. I say that because I’ve noticed that if I sit bolt upright to, say, have a drink for a minute and end up checking my phone messages or whatever, when I get back in the hoods almost without exception there’s been no drops in that period. The only difference would be my cadence slightly lower, torque slightly higher and pedal motion more force on the “down” stroke and less “round”/back. I don’t know how kickr works but I read somewhere (DCRainmaker??) that it measures “chain tension” as a way of calculating both power and cadence (somehow) so - and this could be a stretch - I’m wondering if it can’t properly interpret a smooth pedal action and needs the “choppiness” of a strong down motion followed by slack to read power consistently??
My only other hunch is that I can seem to trigger the issue if I spin fast for a few seconds and then reduce cadence - almost like I “get ahead” of the flywheel somehow (the flywheel is speeding faster than I’m pedalling due to inertia) and it thinks I’m applying no power?
Is anyone else seeing the same? And can anyone who is more technical than me and understands the “logic” of how ERG mode works explain this to me, this isn’t correct behaviour right? Specifically I don’t understand
- If ERG mode is on, the trainer should never stop providing resistance so long as I am pedalling, right?
- If 3 sec avg is turned on, and pwoer smoothing turned on, why is the power reported not getting smoothed out even with this issue occurring? A series of 250,250,250,250,160,250,250 (power readings each second) shouldn’t be possible with power smoothing/averaging turned on, right?
I’d love to hear if other people are experiencing this, not only from people who have answers/suggestions please.
Technical stuff/point to note:
- I am currently using an iPad Pro (iPAD OS). Its patched to latest version. But issue occurred on my last device too so is not linked to the device
- I use a Wahoo Kickr v6 turbo trainer but issue occured on my old Kickr v5 too so doesn’t seem linked to a faulty kickr unit
- I use wireless connection to link Kickr to iPad, but issue also occurs (no difference) when I use bluetooth BLE instead
- Latest version of OS and Zwift, although problem has been continuing for over a year across various versions
- I have tried using the Kickr for cadence detection, as well as a Wahoo dedicated cadence sensor on pedal. Same issue regardless.
- No modifications to Zwift
- No modifications/jailbreak or whatever its called to the OS, its as Apple provides it
- This issue happens even with trainer difficult set to 0%/off so is nothing to do with declines/downhills.
Screenshots to help illustrate:
How it appears in Zwift while riding (in realtime):
How it appears in intervals.icu when its reading the fitfile after ride is uploaded:
A sample of the raw data from the .fit file:
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