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Power comparison with Vector 3 Pedals

muckymariner
over 5 years ago

Hi,

I got my 2T today and did my first ride using TrainerRoad. I used the 2T as the power source in Erg mode connected to TrainerRoad, with my Vector 3 pedals connected to my Edge 1030. There was a significant defference between the power readings of the two devices of between 15 and 20 watts; the Neo reading approx 245 and the Vectors closer to 260. A chart is attached showing hte two rides overlaid on one another.

Is there a problem, or is this normal? I don't know how the different readings are taken, but assume that they should be broadly similar across the range - the variation seems to great to be accounted for by devices at opposite ends of their tolderance ranges to me. Grateful for your thoughts?

https://analyze.dcrainm..aker.com/#/public/1095b96c-676d-43d7-6f98-40b0d3533806

Any advice would be gratefully accepted.

  • 0 over 5 years ago in reply to muckymariner

    Use small front ring and at rear the middle in ERG mode, disable Powermatch in TR, let's control your Tacx by TR and record your Vector 3 with Garmin
    and you get only 6 Watt difference, this is the best you can do.

    In my case i use 34/18 and i use this chainrings/cassette:

    11-12-13-14-16-18-20-22-25-28-32T

    https://www.j-berkemeier.de/gear-calculator.html?kb=34,50+rz=32,28,25,22,20,18,16,14,13,12,11+tf=85+dtf=5+ru=222+vr=3-3+ge=true+rt=true

  • 0 over 5 years ago in reply to f|33tStA

    I also tried the optimal chain line like you suggested and it made very little difference in my case where the Neo 2 was measuring 15-20W lower than the PM. Believe me I tried everything to justify the problem is not the Neo 2, doing single leg drills etc.

  • 0 over 5 years ago in reply to Eric

    how you look for the difference, do you mean the power datafield during the ride on Edge?
    i use a Power 3 sec field, there it looks not so bad, sure, when low power it's not so exact and of course single leg drills coud be different, look on a workout with no ILT and take a look on the avg power, better the NP, normalized power on Edge and normalized power on TR have 6 Watt different on a whole workout

    don't forget rpm arround most workouts on TR are 85-95 rpm, think this cadence is necessary!

  • 0 over 5 years ago

    I've done this a lot. But here another analysis.

    most of the time betwenn 34 -19 and 34 - 28

    Zwfit full control on Tacx nec 2t, Stages on Garmin 830.

    TSS Garmin 50; TSS Zwift 59!!!

    Here are the numbers.

    https://www.zwiftpower.com/analysis.php?set_id=37695

    AWFUL.

  • 0 over 5 years ago in reply to FelipeSerra

     you configured the same FTP in Zwift and Garmin?

    i calculated my FTP difference between Trainerroad (Neo2) and Garmin (Vector 3) with 6Watt difference and my TSS and IF is equal on both platforms then!

    anyway, it looks like you have ~14,6 Watt difference on this workout, so you have to set your FTP different on both platforms!

    if you do a Ramp test or 20min FTP Test on Zwift and record it twice on Garmin you could calculate the difference better

    Your weight settings are equal on both platforms?

  • 0 over 5 years ago in reply to f|33tStA

    same everything.

    So you are working around on this? I don´t want that, i want a precision tool. (1%) I know what to do to...

  • 0 over 5 years ago in reply to FelipeSerra

    i think, thats impossible, don't forget, your power is measured on 2 different points, stages measures on your crank and Neo measures direct on your casette!

  • 0 over 5 years ago in reply to FelipeSerra

    the Shimano crank based only right sided powermeters are underreporting the power (it is a well known problem since year/s/) , this is why You have lower values on Garmin, these only right sided ones are worse then the left leg only versions (the problem is the material of the hollowcrank driveside crank, so the dual versions are also underreporting the power but with a little less due to the left side is usually accurate, only the right side is wrong... and in your case the lower value is doubled for the "total" power) 

    https://youtu.be/M0tWTUwpt1k?t=2


    So this is why i NEVER recommend to my friends/clients such a poor powermeters like this, if You wanna accurate powermeter, buy a Power2Max NG or NGEco which is spider based, have auto-zeroing function , this  Shimano crank based powermeters are cheap toys but not accurate and reliable powermeters (i'm an expert in it, since many many years... ) 

    with a Power2Max NG You will have different also (because the Neo is measuring the power on hub, so it is always less, the P2M on the spider, so it is always higher a bit, and between the 2 points there are drivetrain losses) but it is apprx 4-8watts maximum (depending on used gears and the condition of the chain and drivetrain parts)

  • 0 over 5 years ago in reply to f|33tStA

    No problem here, it's power, where is measured doesn´t matter, just matters where is measured must be precise. You are not measuring something outside of the bike, you are in the same "system".

  • 0 over 5 years ago in reply to Luko79

    Done tests with both sides and left one on MTB. No issues here. The TACX has a precision problem, claimed in different parts, medias, reports, videos, etc.