Baffling Power Meters: For Those Smarter Than Me

For those who don’t understand why someone would want an accurate power-meter this is not the thread for you. Feel free to skip. :slight_smile:

This has been a 3 month rabbit hole that I can’t get to the bottom of. If you have any constructive theories I’d love to hear them. It’s important for me to get this right, the solution may just be upgrading from the Assioma Uno to Duo but let’s give this a crack.


  1. Wahoo Kickr Core reads 12% higher than left side Assioma Uno. Everything has been tested- retested, calibrated, static weight tested.

  2. Using Dc Analyzer: Quarq Crank (friends bike) reads 10% higher than Assioma Uno. That’s 2 power meters that read 10-12% higher than Assioma.

  3. As a test, I inflate Assioma power scale factor by 10% and retest on trainer.

  4. Using TR linked to Wahoo Kickr. And Garmin linked to Assioma pedals. Both power meters (see 1st graph) are now almost identical. BUT RPE and HR are significantly higher. 212w for me is Z2. Typically HR is 135ish. Today it was in the 150’s and I was breathing hard, felt more like SS effort. Note: This is with pedals scaled up 10%.

  5. TR linked to Wahoo Kickr power and Assioma CADENCE ONLY. And Garmin linked to Assioma pedals (graph 2). RPE feels normal. HR is back to normal, and Delta is back to 10% lower on pedals. Note: This is with pedals scaled up 10%, so it’s now a 20% delta as 191w is really 172w but is reading 212w on TR.

DC Analyzer Report

Seems like the truth will only be resolved by buying the right pedal. But at $US500 after spending the initial $500 for the uno I’d love to avoid it.

TLDR; Even with Assioma power scaled up 10% when linked to Kickr Core there’s a 10% delta in power UNLESS TR is linked to Assioma cadence-only sensor in which case power is identical BUT RPE and HR is significantly higher.

The easiest and most obvious possibility is that you have a larger-than-usual leg imbalance. If your left leg is 5 % weaker, then doubling that value means your Assioma Unos will infer a total power = 2 x left power that is 2 x 5 % = 10 % lower.

Did you check your leg imbalance while on the Quarq? The number isn’t perfect since it approximates left/right power, but if you have a larger imbalance, then this should show up.

Overall, I would simply bite the bullet and get a power meter that measures total power, e. g. by upgrading your Assiomas to Duos. Training on a one-sided power meter has caused a severe leg imbalance (5–6 %), although in my case my body was smart-lazy — it upped the power output of the left leg, so for every additional Watt in my left leg, I got credit for 2 additional Watts :wink:


This is all constructive, to get to your objective.

Kickr Core is not a power meter. Forget smart trainers.
Crank is not equivalent to pedal.

So you have one non-equivalent power meter you’ve compared to.

Define “accurate” for you?

What are the manufacturer parameters for the Quark and the Assioma?

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As you can see in the power comparison, you have a L/R imbalance and it isn’t always the same imbalance, and the value occasionally flips in terms of dominant leg. Its just how it is with single sided power. It will also vary with fatigue from day to day as well as during a ride. I gave up on single sided power for training, I still use it for tracking TSS etc but my race bike has a crank based PM that I trust for accurate power


The power numbers by the Kickr Core are just as valid as those of pedal- and crank-based power meters. They just infer power differently. The only thing to consider is that they are further down the chain, literally, so the trainer sees drive train losses whereas pedal- and crank-based power meter do not.

I don’t want to get into accurate vs. precise. But both, Favero’s Assioma Duos and Quarq power meters have an excellent track record. That doesn’t mean all units are perfect, just that on average they tend to give good numbers are are reliable.

However, the obvious issue is that the Assioma Unos are single-sided, i. e. you get all the systematic errors that are inherent to single-sided power meters. Add to that that the Kickr Core’s power numbers match those of the Quarq, and it seems that single-sidedness is the likely culprit.


These statements/questions are for AussieRider to better understand the problem they are facing when they say they want accuracy and truth, by answering yourself you aren’t helping them understand.

And I disagree with your conclusion.

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Yes, and I think you are wrong when you claim that his Kickr Core isn’t giving him “real” power numbers and that they should be ignored. Both infer power by measuring different things (rpm and temperature in most trainers, including Wahoo trainers, with the exception of e. g. a few higher-end Elite trainers) or resistance, temperature and rpm (in any strain-gauge-based power meter).

Trainers measure power accurately, and their power numbers are consistent with known good power meters. So if one deviates from the other, you cannot simply say you discard the trainer.

And why?
I think the Assioma Uno being single-sided plus a leg imbalance is a plausible explanation. And if he has access to the Quarq power meter again, he can check whether he has a strong leg imbalance.

Yes it showed my left was weaker than my right. I don’t remember the exact figures but it was significant. I still have the files. Will report back.
My suspicion was simply that. The left was weaker than the right and the inaccuracy was being doubled.

The other question is: why is the trainer reporting two different figures when the assioma cadence sensor is either connected or disconnected?

+/-2% on quarq, assioma and smart trainer. All three have been proven so by Independant testers. As I said elsewhere the imbalance in legs is a theory. The only real way to know is to get a dual sided power meter.

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While yes, my assumption is a leg imbalance I don’t believe there’s anywhere in the file that reflects this. Especially considering pedals are left power only and trainer is drivetrain based.

We also don’t now why there’s an immediate 10% delta when turning on/off the cadence sensor.

Yup, that’s evidence for the leg imbalance theory.

I don’t quite understand this given what you have written in your other post: you wrote you saw a significant leg imbalance in the Quarq’s power data.

Assuming I understand how you wired everything up correctly (via Bluetoth), it might be that you are simply misinterpreting the data in case 5: if you ask TR to use the trainer’s power data and your pedal’s cadence data, then it will base its workout off of the trainer. Your trainer does not need cadence, it computes power from changes in flywheel speed. Likewise, your Assiomas will still use the built-in cadence data to compute its power, because it computes power from torque times cadence.

So it is quite obvious why RPE feels normal: you are simply using the power data of your trainer to do the workout. Your Assiomas are just passengers here. They could read 50 % high or 50 % low, it wouldn’t change anything.

Perhaps I am misunderstanding your OP, but I don’t think the trainer is spitting out any different numbers. The trainer’s power numbers are what they are, and since TR goes by cadence and the trainer doesn’t use your cadence data, the power numbers don’t change.

On the other hand, if you made a mistake in scenario 4 and you used your Assiomas power meter with TR. For example, one plausible scenario is the following: if you use Bluetooth with your computer/iPad/phone and Ant+ with your Garmin!), then you could have simply used your Assioma’s power data which overrides your trainer’s power data when you use power match. Your trainer will still show up as a power source, but you also need to disable power match. Since your Assiomas read lower than the trainer, you had to put out 20+ more Watts.

Note that Bluetooth connections tend to be quite “grabby”, it is usually first come, first serve for devices. Preventing a device from connecting via Bluetooth when you cannot disable Bluetooth is not easy.

Its not using power match. Tr has a feature to only use pedals as cadence sensor. See image below.

That would explain the behavior you see: in Scenario 5, when you use “Cadence only”, power match is disabled. TR chooses resistance level according to the power data supplied by the Kickr. In Scenario 4, it seems that TR had power match enabled, which means TR ignores the power numbers of your trainer and uses the power lower numbers of your pedals. That means if TR asks you to pedal at 200 W, in Scenario 4 you’d have to do 10+ % more work, because TR won’t stop until your pedals tell TR that you are putting out 200 W.

So yeah, I think that would explain the behavior.

The solution seems simple: in view of your leg imbalance, if you want accurate power data outdoors, you need to upgrade to Assioma Duos. Or some other power meter that measures total power.

If your left leg is 5 % weaker, then doubling that value means your Assioma Unos will infer a total power = 2 x left power that is 2 x 5 % = 10 % lower.

I don’t think that’s correct. Say your true total power is 100 such that, for a balanced person, each leg produces 50. Then 5% weaker than balanced (50) is 47.5… doubled is 95, so 5% below true power.


You are right: I was basing my calculation off of a 45:55 left/right split. The difference is indeed 10 %, not 5 %. Thanks! :+1:

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that 5% coupled with the fact that all power meters read a little differently could together explain the issue.

I believe there was another post made regarding assiomas and KICKR, which I responded to.

I have assioma duos and a KICKR V5. My KICKR reads power a little higher than my pedals by about 5% or so. I am not sure why.

Never having owned a set of Assioma’s, I have no idea how you would do this, but my guess is that whatever you did, didn’t do what you think it did.

I think I am right in saying that if you don’t select the “Cadence only” option, TR prioritizes power meter power over trainer power. So I think TR was recording power from the Assioma, and so was Garmin, which is why your graphs match so well.

With “Cadence only” selected for the Assioma, TR is recording Kickr, and Garmin is recording Assioma, and your average power is ~25w different, ie your 10-12% mismatch is still there (see point 1 above). The 25w lower AP for this session probably explains the HR/RPE difference as well.

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Yes. Didn’t think of that. By disabling cadence sensor I’m enabling power match which means I should have “forgotten” the Assioma’s on TR all together to get a true comparison. However! If we started with a 10% delta. I then Added 10 power scale factor to the pedals. Shouldn’t the power match number now be the same as the trainer as we’ve inflated the reported power of the pedals?

I agree I think this is the only way as it seems by adding 10% power to the pedals it feels 10% easier outdoors but still 10% harder indoors. The 20% delta has become a mystery that I’m just not smart enough to solve.

You’re right. It’s a common confusion. What he means by 5% is 45/55 which is what I suspect.

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Genius. I knew I messed up somewhere. It’s doesn’t explain the 19% added power scale factor. Which I talked through with Favero tech support. Basically with the theory that my leg imbalance was 45/55 I added 10% to the left pedal to bring it more in line. I did a 90 mile ride outdoors yesterday and power was definitely reading ~10% higher. Usually I cruise at 200w HR 135. However, I was cruising at 220 with same HR. And on climbs. My friend who weighs more than me was pushing 10% less watts on a climb as we ride side by side.