If you have even the slightest interest in power meter and trainer inaccuracies, you’re going to find this immensely intriguing (@GPLama, I’m looking at you).
Here’s a workout from yesterday. All details are available here. TrainerRoad is controlling the Kickr, but without powermatching in this case. The purple is the Kickr, and the blue is my Assioma Uno.
As you can see, whenever an interval or rest period begins, the Kickr and the Assioma disagrees for about 40-50 seconds, when they suddenly get back on track. What’s odd is how incredibly consistent this is. Here’s how this looks zoomed in on the beginning of all recovery periods:
It’s the same with the work intervals. They all look like this:
Most of the time, I can feel these jumps in power, so I know it’s the Kickr that is adjusting its intensity, while the pedals simply record the reality. You can also see this backed up by heart rate and cadence:
Here’s a different workout with powermatching.
Because the pedals see that the Kickr is starting the interval too high, powermatching adjusts things down for a while. Then, after 40 seconds, the Kickr is getting accurate again, and the pedals see that the intensity is now too low. Powermatching does its job and basically brings the intensity back up to where it was supposed to be from the beginning.
I got 99 other power accuracy problems, this ain’t one of them! I’m deep into other work at the moment so I can’t give this reply too much attention… but quickly…
You’re comparing x2 left (UNO) to Kickr Core (total power). So you have another variable to factor in, balance.
You’ll need to play the game of removing one variable then resteing. (Then repeat until you’ve got enough data to question why companies even bother with accuracy claims. /s).
Sure, this is a single-sided pedal. Still, I’m pretty sure I don’t consistently change my power balance 40-50 seconds into an interval or rest period. Again, the pedals and trainer track relatively close to each other except when the Kickr gets thrown off by a change of intensity.
It looks to me like there is some sort of auto-calibration going on in the Kickr firmware, I just find it odd that I haven’t heard about this “feature” elsewhere, and how it’s so consistently off for an almost exact length of time until it corrects itself.
I’d take a punt you’ve found a bug or some combination of weirdness. I’d replicate the same setup/pairing/intervals on another platform or with another utility. If it still occurs, then it’s not the TrainerRoad trainer control. If it doesn’t occur then it’s one for TrainerRoad Support to dive into.
Good point. I think I can replicate this just by doing a workout in Zwift. I’ll do that and post back.
OK, I did an ERG workout on Zwift tonight. Did I see the same behavior from the Kickr? Yes, I did. The full details are available here. And this is what the workout looked like:
The phenomenon shows up on all the intervals and recovery periods. Here’s the beginning of the final interval:
That’s 40 seconds until the Kickr sorts itself out. And here’s the cooldown at the very end:
Again, 40 seconds.
And yes, the Kickr is showing some general inaccuracy as well on this workout, but that’s beside the point. I didn’t do a spindown today, but I did do one at the end of yesterday’s workout. The first interval is particularly interesting. The Kickr tends to inflate the power values as the cadence rises. Subconsciously, this makes me spin at a higher cadence than I normally would, because the actual power I need to put out becomes lower. A little over halfway through in that interval, I decided to lower my cadence to see if the accuracy would improve, and it did:
And before you ask, no, the power jumps I see after 40-50 seconds are not caused by me consistently changing cadence at that point. That’s clearly demonstrated by the second interval:
What I find so puzzling is that the base accuracy of the device is OK (not great, but good enough). It’s just doing this strange thing until it manages to sort itself out. And it always does so after 40-50 seconds. And although lots of people are asking questions about accuracy, I have never seen anybody else mention this particular issue.
I am getting kickr core dropouts during form sprints, both power and cadence disappear. Wahoo have made me do lots of tests, spin downs etc. It appears that my kickr drops out around 50mph. Not sure if this is related to the issues mentioned here.