Hey guys,
Can someone point me to another thread or tutorial as to how to compare power meter accuracies? I think my pedals are under reporting by over 20%.
Thanks.
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Comparing Power Files Using ZwiftPower
ZwiftPower has a tool accessible under Your Profile>Analysis which makes comparing two .fit files from two different power sources easy. If you’re registered on ZwiftPower the site can already see every Zwift session you’ve ridden – so all you need to do is upload the second file from your computer and you’re good to go!
Here’s what the process looks like:
- Finish and save your ride (on Zwift and your bike computer)
- Click Analysis>Create New Data Set from your ZwiftPower profile page
- Select your activity from “Use .fit file from Zwift Activity”
- Choose which power source was used for your Zwift activity (or enter the name of a new power source)
- Optional: assign this analysis to a Zwift event you entered by choosing the event from the corresponding dropdown
- Add a comparison file from your computer, and select which power source to associate with that file (or enter the name of a new power source)
- Click “Create Data Set”
This will take you to a page showing a graph of the data from your two power sources. You can now fine-tune that graph if you’d like using the Time shift and crop tool. If perhaps you started recording your ride on your computer a few seconds after your Zwift activity began, this tool lets you easily shift the data by X seconds. Just enter the number of seconds in the “Offset” box and you’ll see the graphed lines move. It may be helpful to zoom in a bit so you can line up the two sources nicely, then just click “Reset Zoom” at the top-left to see the full graph once more.
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Thanks. I don’t have a Zwift account, only TR. I was told intervals.icu had a tool that would work with TR?
Have same setup. I connect my assiomas to wahoo bolt and my kickr to wahoo app on my phone and hit start on both devices (bolt is only recording and phone is controlling your kickr and recording). I ran some simple intervals on different powers like 100w,150w,200w,250w couple of minutes on each and then compare in intervals both workouts.
(btw to fast check you can connect assiomas and kickr to wahoo app, on the main screen under the connceted devices fhere will be actual power reading for each so it is easy to spot the diffrence)
Most of the time it is Wahoo kickr to blame not assiomas.
-For me any firmware above 1.0.13 is very unstable and i got problems with correct power, so i downgraded to the older one.
-Kickr can get hot when riding hard kntervals and can be not accurate then, it is worth to put your fan so it blows at least a little the trainer. (again with older firmware no such problems)
-factory calibration helps (but for me only with older firmware, the new one even after several factory spindowns is very inacurate on higher loads)
-you can chek/manualy calibrate your assiomas to. You need a kithcen scale, some training weght like 5-10kg, some cable. But it is supposed to check/correct the diffrence between l/r pedal and correct samll 0,5%-1% inaccuracies and not 20%. Again Assiomas are like 99% correct most lf the time
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I’ve used DCRainmaker’s DCR Analyze Tool to align fit files and compare power readings from pairs of power meters. It works very well. link - DCR Analyzer
Robert
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Are Assiomas dual or single sided, as L-R imbalances can be significant
And if it’s the Kickr that’s the issue (not that you can easily tell from a sample of two… you could check actual vs estimated power on some long, steady, sufficiently steep outdoor climbs - you don’t want much wind resistance), you can actually have the Kickr use the power from your Assiomas (assuming they are always on your trainer bike). There’s a setting in the Wahoo app to connect an ANT+ powermeter, and it then just uses that rather than Kickr as power source (also for erg mode). FWIW I find the Kickr accurate in general, assuming calibrated every couple of weeks
This in incorrect. There is no tool in intervals that can do this. There is another free tool which popped up on r/Velo sub Reddit the other day but I have not tried it out. Might be worth a look:
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Yes. Intervals would work w/ TR if you feed the data from TR into intervals. I believe the best way to do that would be to sync TR data into dropbox and then link dropbox to intervals. (as Garmin now doesn’t forward data that is not recorded via their devices - actually, many companies are not doing that anymore - Strava also did try, tho they backtracked on that)
In terms of what you want to achieve, comparing power meters from within the same FIT file, that’s not doable AFAIK. Tho as others and myself has indicated, there are other tools you can try by using 2 different devices to record the data.
Or if you have an iOS device, you can try this app I wrote (https://forum.intervals.icu/t/breakaway-indoor-training-app-now-with-intervals-icu-calendar-integration-workout-of-the-day/) and use the below option within settings. This will both plot the data on screen (your Smart Trainer Power and your Assioma). It will also output a simple CSV file you can export into excel/google sheets and play around w/ the data. (The data is all sync’ed up so you don’t have to do any maths to line it up)
I added this feature for powermatch to calculate a fixed (average) offset and to look at my own trainer vs my Assioma. (eventually i found out that basically, my assiomas we so accurate or my pedaling style was so bad that there was quite a lot of variations in my power.
if you do try the app, let me know what you think.
Most power meters have a tolerance of +/- 1-2%, so if one is at +2% and the other -2% you will have a 4% variance. There will also be a drive chain loss at the trainer vs cranks or pedals. Then a L/R imbalance can further skew the variance, but this can be compensated (offset) if you have sufficient data from steady efforts on a dual sided power meter (I’ve used a Watt bike for many sessions before acquiring a PM, so I know I’m 48-52 when I don’t focus on my pedal efficiency but 49-51 to 50-50 when I do).
This loss is made worse with a dirty chain and a “cross chain”. ERG mode should be disabled, as soft pedaling for a few seconds would also show a variance.
A step test (in resistance mode) for 1-3 minute durations would be ideal so that the power is steady for a period of time.
I have seen 2-3% variance at times as well as 10-15%.on the same workout (4iiii Kickr Core). I’ll always do my testing on the same PM on the same route (outside) or setup (inside).
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If you have a Garmin, then the ANT power meter datafield allows you to dual record so both PMs appear in your FIT file.
My Wahoo Kickr v4 matches my Favero Assioma Duo very very closely within 2 to 3 w while my Wahoo Kickr V5 over-reports by 15 to 20w. I did this comparision because as soon as I moved from the v4 to the v5 I started getting suspicious higher FTP alerts in RGT, Zwift and Intervals.icu when riding on the v5.
(I have since returned my v5 to Wahoo and stick with the v4)
As I said earlier probably the software and factory calibration is to blame. I had a power difference of around 20w-30w and wehn my Core started to make some noises i got new replacement unit. The new unit was spot on with my assiomas (like 2w difference). For a month i was avoiding any updates (was scared of new problems commming and was very happy with the reading and overall how it works) but one day just by accident i updated, and ofc all problems came back and on top of it my kikcr started to kind of giving different resistance then it showed on the app (i put 200w in erg mode at wahoo app but the same wahoo app was showin that I’m riding at 180-190w). After several factory spindowns i gave up, downgraded the firmware as the last chance before sending for replacemnt, and now it is spot on with my assiomas as earlier and is holding power as it should. It’s pretty common problem i think at least I saw couple of posts on facebook groups. I think that noone at wahoo thought you would compare your kickr with proper power meter and most of people using it doesn’t even know it is reading wrong power. Only positive is, after some husstle at the end it is possible to make it read power very close fo assiomas (like 2w)
This is how I compare with Garmin - the Power2 field is written by the ANT Power Meter datafield.
Note Garmin tries to match the peaks by applying -20 to the scale on the left. This example is from the Kickr v5 which was inflating my power vs. the v4 and Assioma Duo.
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Assioma’s are single sided. Issue is, when using the pedals outdoors, 300w feels like 300w. When using them on the trainer it feels substantially harder. When I compare numbers through TR, @ 300w the kickr is reading 360. I know I can hold 260w for 45 min up a climb (in the middle of a 4 hour ride) . Using the very same pedals on the same bike on the trainer and I can’t hold 260 for more than 5 min. In fact doing a ramp test yesterday, with 1 min increments of about 20w I was struggling to hold 280 for 1 min. And my ftp is between 265-280.
I’m going to compare the two tomorrow. But I think the kickr may be accurate. Only because the power on the kickr, and the pedals outdoors feel about right. but when i connect the pedals to trainerroad it feels 20% harder / reads 20% lower.
Wow! How do you dual record power? Thanks!
I’m getting a 20%+ Delta. But, it just feels like the issue is when using the same power source from outside to inside. Like the pedals read wrong indoors, but right outdoors. I can’t hold any power using the pedals indoors it’s like 300w feels like and reads on the kickr at 365w.
I’ve used two computers, one connected to my Quarq and the other connected to PowrLink pedals or KICKR, . I then upload both fit files to quantified-self.io and merge them. Then can compare data collected from both head units and power meters.
I mean the power reading from your kickr is controlling your trainer, assioma is just showing your power. Assuming assioma is showing 260 and it is too hard to ride indoors that means your kick is reading much lower not higher numbers (common thing for kickr) and is rising the resistance to compensate the lower readings. But hard to tell (i cant fully understand what is showing what in your situational)
Please open your wahoo app conncect kickr and assiomas, set erg mode to 200w or 250w as you like and please record this screen as you ride for couple of second a minute or so at steady pace (make sure all other apps like tr are closed and powermatch is disabled)
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Assuming we are talking Assioma Duos then as these are two independent PMs, as long as your left / right balance is close to 50-50 as duos are essentially cross checking one another, I think we can always trust these readings vs. a trainers PM
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