Did the comparison using both Kickr through TR and Pedals through bike computer (link below). Difference was ~10% lower on pedals. Far less than I had experienced during the ramp test. Being one-sided I understand that this is within acceptable tolerances. Really appreciate you helping out.
https://analyze.dcrainmaker.com/#/public/4ef4db89-1a86-416d-6dd6-ed7877896a8d
Be careful, comparing power between different power meters can get one to question the true nature of reality, what is real, and maybe even the meaning of lifeā¦ 
When I got a Kickr Core I compared it to my Stages PMs (2) and found the kickr 10% low. And compared to a Power2Max and found it ~7% low. Though the differences did vary with power output (higher power output meant more difference.). Clearly something is wrong if my Stages (stated 1-2% accuracy I think) and kickr core (stated 2% accuracy I think) are that far off. At least the P2M (stated 1-2% accuracy) was within margin of error with my Stages. Thats all with calibrated / zeroāed / spun down equipment. I go with my on-bike power meters as āthe truthā so at least I have the same numbers inside and outside.
Fortunately I pulled myself back from the the path to madness that is questioning: what is real? are any of my PMs getting the ārealā power? how can I tell?
I guess, for me, it doesnāt matter what the number is. As long as I know with good confidence where my threshold is- both indoors for training purposes, and outdoors for racing purposes. The question was are my pedals reading differently when switching between trainer and outdoors.
The rising drift especially in intervals 2 and 4 is noticeable. My guess would be a shift in right/left leg power depending on power/duration and so on.
Additionally you might test to recalibrate kickr during ride (calibration when kickr is heated up). And riding in very easy gear (low flywheel speed of kickr, less heat, easier power control for kickr with lower power amplitude). But maybe you already considered that.
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I did a 10 min warm up before hand at 160w and recalibrated. But I guess I didnāt really get it that hot. I could also recalibrate after a workout but would that mean it would be less accurate at the beginning of a ride? Thank!
I havent read all the posts but has anyone mentioned that the kickr measures at the rear wheel and the pedals measure at the legsā¦what is there 5-10% loss through the drivetrain?
I did an analysis of both this morning and thereās a 10% delta, far less than what I thought I had during the ramp. Not sure why. Could be heat, could have been me. Being a single sided metre I guess this is totally acceptable.
It better not be 5% or more unless you have a really bad chain and lack of any decent lube.
2-3% based on this article.
Itās about 10%. See link below. My chain is about as clean as a wet lube chain can be. chain has 1000 miles on it. dry conditions. Fully degreased every 200 miles. My guess is a combo of both measurements being out a couple % + a possible left/right leg in balance on the single sided power metre.
https://analyze.dcrainmaker.com/#/public/4ef4db89-1a86-416d-6dd6-ed7877896a8d
I was specifically replying to the comment suggesting that pure drivetrain loss could be 5-10%. Based in that article I linked and others Iāve seen over the years, its unlikely to be that high and not the core issue for you here.
Stacked tolerances between each PM, and the single vs full are the more likely contributing factors here, just like you said.
Totes, thanks for your input, tāwas really appreciated. Not sure why the ramp test had a significantly higher delta. Hopefully itāll settle down now. I think Iāll stick with the Kickr reading for this month and give next months ramp another crack on the pedals. Alas, my FTP (and ego) will drop by 10%). I wonder if AT will read that switch as a loss of fitness or recalibration of sensors, or more importantly whether itāll matter.
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Yip, I feel AIFTP is biased by my upright riding on the road bike, where as I use my FTP for pacing TTās more. I also feel that whilst in the TT bike on a steady trainer I can push right to limit I wouldnāt be comfortable safetywise for outdoors, so thereās a little took off for that. Perhaps that is why I am not at the āmeaty endā of results
I would think a 10 minute warm up then calibration should be āgood enoughā, although calibrating after a workout or after a longer/harder warmup is worth trying as well.
I looked at the data, and it is 10-ish % for most of the workout. I would use the Assioma app to increase the power by 10%, and then re-do this test, as things then should line up fairly closely across the workout. As has been pointed out, with just 2 meters, there is no way to tell which one is ācorrectā, but with the adjustment that Assioma offers you should be able to get both your power sources to report very similar numbers.
It would be worth doing this type of comparison over a few more rides, as I have seen notable ride to ride variation on my previous setup, but I donāt know how common that is.
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Do you mean you can recalibrate the Assiomaās to report 10% more power than is reading? If so do you know a resource to direct me how?
I just did a 90 min threshold workout and compared the two again. On the last set of Over Unders the Assiomaās read 13% less output than the Kickr Core.
I have a 2017 Kickr, which was the last model before Wahoo introduced the Core. For what its worth I saw ride to ride variability in the offset between bikeās strain gauge power meter and Kickrās optically-based power estimation.
Thanks, just retested on a 90 min Over Under Ride. The delta on the last set was 13%.
https://analyze.dcrainmaker.com/#/public/b053f326-7022-4a4d-5c52-7960320fb88b
It is in the assioma app under settings. Canāt bring it up on my phone right now, as I would have to connect to the pedals to get the screen up.
For me this is a required feature of any future power meter I get, as otherwise having multiple that read āclose enough togetherā is a gamble.
It seems my 2017 Kickrās estimation accuracy is related to time, suggesting it might be impacted by the heat of flywheel. Iāve seen the Kickr go + and - relative to the bikes PM. Over time I kept tweaking my setup to make inside as close to outside as I could get, which led me to using either Sim mode or Level mode (which I believe TR calls Standard mode).
This would really appease my ego, assuming my FTP is 13% higher than my pedals are reading. Iām just not sure I could live with myself. Lol. Or maybe I could? If only I had a third reference point. Do you know if one Garmin head unit can record two power devices at the same time? If so I may be able to borrow a friends bike to test.
I donāt think 1 device can record 2 power meters, at least not in a standard way that will be read by the DCR analyzer, etc.
As much as we all want to know our ārealā power numbers, I would focus on getting your two devices to read the same, as this is much more important for training, etc. If you end up confirming that the pedal is correct, and the kickr wrong, you have no way to change what the kickr reports (like you do with the pedal.)