Power comparison with Vector 3 Pedals

ah ok, clear! 

As i told, usually those are posting who has complaints about the difference, and usually the pedal based powermeters (or the single sided cranks but there the missing right leg data is the main problem mostly) have the most problems, and i have seen more faulty (or with wrong settings) bike powermeters than faulty Neos. for example your friend's 1watt difference is also problem because it is too less (and sometimes a bike powermeter is showing LESS than the Neo, that is most fautly setup :) , there is no such a low different between the 2 points , so probably his pedals are measuring low. :) Yes, from the "big data" easy to find similar results and telling , it is same as mine so we have common issue (but it is not true everytime ) 

and yes, maybe (as i wrote too) the oval is "adding" a few fake watts to the Duo's measurement.  

Well for example,

The guy posted this: https://www.zwiftpower.com/analysis.php?set_id=33789 , he has the duo.. looking at the graphs, it looks pretty much the same discrepancy as mine. Which makes me think it can't be that both our pedals have the same problem, however the cadence as you said seems to be higher in his case also. Hmmmm I'll have a check with Favero why this is happening. 

yes, and this lady has only 3-4w difference with 2T what is the normal : https://www.zwiftpower.com/analysis.php?set_id=67714 btw, she has the cadence difference too :) and if You find a triple recording like this (unfortunately Kickr ...) : https://www.zwiftpower.com/analysis.php?set_id=67290  there is the same cadence difference between Infocrank and Duos , and here the Assiomas are reading low, the Infocrank is a very accurate pmeter, using it as a reference one if it is newer model. 

Of course we dont know every details about her/his setups (as we dont know your posted guy's neither) but we can make "half"conclusions.

The lady is doing it in sim mode, I forgot to mention this issue seems to be quite specific to ERG mode, because in simulation mode my watts are very much closer to the ladies results, which makes me think it's something with Neo 2t otherwise I would see discrepancy all over the tests most likely. 

But yeah it's driving me bit insane as I would like to effectively train with similar data. 

okie, if You have the SIM mode comparison , just let me know (even in privat message here), i'm curious about the result. I suppose You are running on 0.0.36fw in 2T. and dont forget the single leg test in erg mode! ;)

I notice similar results with pedal based power meter (Vector 3 dual) showing up to 4% higher readings than NEO 2T (both devices are claimed to be accurate within 1%). Latest firmware on both, connected via ANT+. Vector 3's after static calibration (with 17kg of weight). Would be too simple to say its only drivetrain loss deriving difference. Garmin should address this problem for sure in the future firmware release.

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sakis MT said:

Would be too simple to say its only drivetrain loss deriving difference.

I am not an experienced cyclist, but would like to understand why you expect the same result when you measure something with two different devices, at two different places and with two different methods. And actually, you measure two different things.

Let's suppose the trainer measured exactly the same power values as the Vectors and you are very happy with that. Now, you change your bike with an old or a different one but still using the same trainer, the same Vectors. Would you expect the same result?

It is a totally normal difference, i dont know what You expect and why (i know the reason but i dont wanna be rude )  there is no problem here to fix.

I'm aware and understand the difference in power measurement place. I think though that despite where power is measured, in all cases it is always transferred from our body in one point of contact with a bike... the pedals. So even though NEO 2T measures the power in a different place it should use some kind of algorithm to compensate the drivetrain loss and minimize the difference showing the power where it is in reality transferred/produced and not measured. Of course I know that different drivetrain may have different loss but it should not vary a lot. I'm not an expert but such algorithm could be one of the solutions. Not perfect probably but minimizing most of the differences.

At the end I generate the same power in a given time despite where it is measured but my speed in training apps like Zwift is a bit different depending on which power source I use and it shouldn’t be like that, at least this is my expectation.

But this "compensated difference" could be 3-4watts till even 10-15watts on a fix 200watts depending on the used bike parts.(chain, bb, chainlube, crank torque to the bb, gear ratio, jockey wheels, etc) How should the trainer guess what kind of "compensation factor" needs to be used?

So usually there is 2-2.5% minimum (but can be even 4% too) between the rear wheel and the crank, so your comparison chart between 5-20mins, /the shorter parts on the CP graph depending on the sprint watts and its capturing timing and heavily modify these short time periods, better to see it directly on the power chart and not on the CP chart/ is within the tolerance imho (i met a "few" comparisons in my life)

Btw, a Vector3 is not a gold standard reference, the 17kg weight (even if it certified weight) is not enough, apprx 40kg is needed for the most accurate static calibration. But it is still static and not dynamic calibration. A very few powermeter manufacturers put their (highend) power meters to this dynamic torque calibration bench (after static calibration) make the powermeter more precise and accurate.

+-1-2% wont change your speed "drastically" in Zwift , it is nothing, maybe a few secs on a AdZ 50-60mins climbing.