The real solution to all these issues is to just use a single power meter for all training. If you really have to use 2 or 3 then you are going to have to go through the pain and suffering of making them match.
2 Likes
Check the crank length configuration in all apps. The crank length set in the assioma app only controls the default - this will be overridden by any crank-length aware apps/devices that connect to it. It is possible that this setting of the crank length happens even when just connecting for cadence only.
Great advice… I just switched my pedals from one bike to another that had a 10 mm crank length discrepancy. As much as I would like to think that my fitness improved substantially, alas, it was because my assiomas were accounting for a different crank length!
1 Like
As a corollary to this, you can also use crank length as a way to add a fudge factor to get power meters to agree. For instance, for my Powertap P1 pedals, I configure the crank length to be 185mm on my 175 cranks, as this puts it in line with my other meters. Note that this isn’t possible with all head units - Wahoo doesn’t really allow this due to their simplified user interface, but on garmin you can enter arbitrary values which gives you more options.
Thankfully the Assioma’s have a scale factor so these tricks aren’t needed. I think all power meters should have a user accessible scale factor.
1 Like
Do you mean dual sided or drivetrain base vs single-sided? If so both Qarq and Kickr were within 2% but Assioma was 10-12% down on both.
My discrepancies are immediate on both the Kickr and Quarq vs Assioma.
Thanks for your suggestions. 
I’m not looking for them to match. I’m looking to find out the actual output I’m doing with a fair degree of accuracy. The goal is to use the Assioma’s for both bike and trainer but the pedals are reading - 12% output compared to 2 different sources and that’s a significant difference in Kj’s over a 4-6 hour ride. Is it accurate? Or is my output 10-12% greater? If it’s accurate then great, let’s go with that if it’s not let’s make the changes and use the pedals everywhere.
Power meter data you cannot trust is useless. The other thing is that the left/right split is usually not constant. It can change with power level, fatigue, etc. When I made the conscious effort to rectify my imbalance, I noticed my right leg would fatigue more quickly than my left. So during later rest intervals, I’d get 57:43 power splits.
2 Likes
Does TR have a crank length setting? My assumption was the Kickr Core would send whatever measurements it has to TR. Assioma cranks are set to correct length.
100% while standing my assioma’s are within 2% of Quarq and Kickr. While sitting it’s 10-12% off which is why I need the right pedal. But why the pedals still read 10% off while seated after inflating the power scale factor by 10% is baffling. I think it’s just time to bite the bullet and by the right pedal once and for all!
What’s odd is that the power goes off at 1hr, almost exactly. Before that hour, it’s fine. Did you rezero something? Did you take a break? move a towel? spill something?
Yes. At one hour I shifted from the Assioma as the power source to the Kickr Core. It was an endurance workout and I was struggling when going off the Assioma’s. By switching to the Kickr my HR dropped 15 beats along with my RPE. Bare in mind the assioma’s have been scaled up 10% in order to compensate for the 10% delta between the two. I had assumed this would resolve the issue. As mentioned above, ultimately I’ll use the Assioma’s for everything. But I still want to know with confidence is 400w 400w or is it ~360 or ~440?
Here is todays SS workout you can see the delta is even at between 7-9%. Even with the Assioma’s bumped 10% already. Before the bump the delta was 10-12%.
https://analyze.dcrainmaker.com/#/public/1e1217ba-29f1-4b55-4596-481d74ea7ba2
I see. Can you send a pic of your drivetrain in the gear you were using? And a pic of how the Kickr is positioned?
Can you add the cadence to the graphs?
The Kickr just guesses power based on the flywheel spindown. Was the kickr warmed up when you did a spindown? It has to guess how much magnetic resistance it’s giving it on top of that. Are you using the right power adapter for the kickr? Try doing a constant power workout in a really low gear and another in a really high gear - this will tell you if the Kickr is measuring it’s resistance well.
It also has to add back in drivetrain loss, which it just guesses something like 5% - which I’m sure someone mentioned. If you’ve got the trainer or your drivetrain out of alignment, use a weird gear, have a bad chain, or have a bad bearing, it’d be easy to get out of whack.
Is the power off at all power levels? Just low? Just very high? This will tell you if the PMs strain gauge is setup right or the pedal is broken.
1 Like
You can see Cadence along with all other data on the links below.
Kickr warmed before spindown. In regards to gear change will have to try but a reminder that using a quarq meter in conjunction with the assioma’s also showed a 10% delta. Power is off on all levels as seen in links below.
https://analyze.dcrainmaker.com/#/public/1e1217ba-29f1-4b55-4596-481d74ea7ba2
https://analyze.dcrainmaker.com/#/public/0eea454c-f7e5-488f-4422-afe4135b6266
The Kickr doesn’t guess power, it measures flywheel speed and infers power from the energy balance equation for the flywheel. The spindown allows your trainer to measure losses due to friction, which then enter the energy balance equation. Knowing the friction term, you can then accurately compute power from the energy balance equation for a given resistance. No guessing is involved here.
@AussieRider did something much better than that, he recorded power with another power meter and used @dcrainmaker’s tool to compare the power numbers. He posted the power numbers, and looking at the data the agreement between the Quarq’s and the Kickr’s power numbers is almost uncanny. Even cadence is almost perfect.
Your drivetrain looks very clean 
Puts mine to shame.
I also had a look at the power files. The agreement between the Kickr and the Quarq is almost uncanny. If you really zoom in, you can find very minor and very short disagreements between the two. Judging by the heart rate data, it seems that the data has a slightly different (time) offset. But apart from that, the data seems to be in as good an agreement as you can get.
2 Likes
FWIW my kicker core reads practically the same as my power meter.
On your issue, there may always be some differences between power meters, irrespective of which type. I understand that this is why some pros use multiple PM during Zwift racing.
Why not just use the assioma as your primary PM and forget about the core? That way you can read the same PM outside and inside.
What is more, you can leave your setup like it is and add your assioma Ant ID in the wahoo app for the core to control power based on the assioma. This basically ignores the wahoo power numbers altogether. Just turn of power March in TR.
Makes for a smoother ride for me.
As should all turbo trainers or training apps. Being able to do this in the TR app would go a long way to solving a lot of these problems.
1 Like
No need to overthink this one. Quality standards in powermeters are like street food. Can be great, or can poison you.
If two devices agree against a 3rd one, outlier has to go. Nothing to deep dive into.
The goal is always to use the pedals both indoors and out. The issue is not having two different numbers it’s not knowing which number is relatively accurate. If pedals are reading 12% low/high there’s no way to calculate total Kj expenditure or your total caloric output is. This may not matter to some but over a six hour ride I’d like to know. I also have goals. Am I currently (approx) 4, 3.6 or 4.4w/kg? Do I have a 1000w or ~880w sprint?
1 Like
Then use power match and the data will be the same inside and out.
Do you really know this? Caloric expenditure is approximately 1 cal = 4.2kJ, and the human body is approx 20-30% efficient. Thats a pretty huge window…
Using 1 single power source, ie the Assiomas and power match. The actual number becomes arbitrary.
Definitely not hypothetical. When I switched from my 4iiii to my Quarq power meter, my Quarq told me my leg imbalance was 55:45. When I got fatigued, it would dip down a bit further.
I am now back to approximately 50:50. Some days one leg is more dominant than the other, but not by much.
2 Likes