Wattage discrepancy between Zwift and Vector 2 Pedals

(Jack Kolpen) #1

I am running Zwift on a flat panel tv (and PC) using a long USB cable with an  ANT +.stick on end to collect a signal from  a Tacx Neo Smart trainer.   I am also running Vector 2 pedals with an Garmin Edge 1000.   It seems like the wattage on Zwift is wildy overstated at times and much higher that Vector 2 all of the time.  In addition, cadence readings are closer but not the same between Zwift and Vector 2.  Any explanations out there for these discrepancies?

(Matt Canna) #2

try switching to 3 second power in zwift.  Chances are your garmin head unit is on 3 second power and your zwift is on instantaneous. 

(Stef Levolger) #3

Zwift does nothing else than read the power and cadence values provided by the paired device. As Matt points out, smoothing may play part in this.

However, you’ll also have to bear in mind that you’re always going to end up having power fluctuations between power meters. Some power meters are known to overestimate power levels, in particular at lower (sub-300 levels).

What you can always do is simply pair the Vector 2 to Zwift, rather than the Neo’s power meter.

(Jack Kolpen) #4

Zwift is already set to 3’second average.  One more data point.  When I pair the Neo with the Edge 1000 I am not seeng the wild wattage and cadence fluctuations.    I don’t want to pair the Vector 2s with Zwift since I’d lose some Neo functionality - like auto resistance, etc. 

(Jack Kolpen) #5

So all of this makes me ink the issue is on the PC end

(Noel Nunkovich *USMES*) #6

For whatever it’s worth, and just as a potenial point of comparison, I have a Neo and both road and TT bikes have Quarq Riken crank power meters. When using Zwift I have Zwift showing power from the Neo and my Garmin Edge 520 showing power from the Quarq. Unless I’m at really low wattages ( <70, for instance), my the two power readings are usually within 7-10 watts of each other, with the Neo generally being the higher of the two.

(. TomH..) #7

Hi all, 

Jack - Is the Tacx NEO running the latest firmware? That could be the problem.

Also in Zwift you can use the NEO as a controllable trainer to get the resistance and your pedals as the power source.

Ride On!

(Jack Kolpen) #8

Yes,  I have the latest firmware.  I also understand that the Neo is it controllable trainer which is why I purchased it. I changed the USB extension cable I was using, then the issue got a little bit better but still a problem.

(Noel Nunkovich *USMES*) #9


Yes, the Neo can be used as controllable trainer with the pedals as the power source, but as far as I’m aware that still causes Zwift to prevent the use of Erg mode for workouts. Has that changed?


(. TomH..) #10

@Noel - Yes you’re right the ERG mode won’t work in this case but we are working on it.

@Jack - How long is your extension USB cable? Some, especially long cables can cause problems due to high electrical resistance. 

Also what Ant+ dongle do you use? 

(Jack Kolpen) #11

Let me be clear that I am having 2 problems. First, when I am using the Neo for power paired with Zwift, the wattage and cadence readings are fluctuating a fair bit. Second, power readings I’m getting from my Vector 2 pedals paired with an Edge 1000 are substantially different than Zwift/Neo readings.   As a further data point, when I pair the Edge 1000 with the Neo  I am not getting fluctuating wattage and cadence readings.   


 My TACX firmware is up to date.  I’m using the smaller Garman Ant+ that came with Vector pedals.   I’m also using a 16 foot Tripp Lite USB cord with a repeater.  I replaced  this USB corded this USB cable yesterday which made the fluctuations a little better than when I had a lower quality approximately 8 foot USB cable.

(. TomH..) #12

Ok thanks for clearing this up. 

  1. Power fluctuation - In Zwift settings you can choose to display instant power vs 3 seconds average power, can you check that if that helps? ( your garmin is probably showing 3 sec. average power - you can check that in settings)
  2. Power diferences - How big is the difference? Bare in mind that Neo doesn’t have actual strain gauge so it might be a little off.
  3. One more test you can run is pairing the Neo through a Smart phone using Bluetooth click HERE for more info.
  4. And lastly - Try not to use any USB extension cable and bring the NEO fairly close to your pc (3 - 6 ft) and see if anything will get better. (The active USB cable might be causing the problem too) 

I hope it helps, check it out and let us know how it went. 

Thank you

(Benjamin Kessel) #13

hey folks, I’m having a similar problem and I’d really appreciate your help.

Just did an FTP test on Zwift with my Powertap pedals.

I recorded the power pedals through zwift with a USB extension and also recorded them on my forerunner 920.

the 20 min avg had a 10% difference between the twovwith the forerunner reading being the higher one.

This is surprising to me since both readings were from the same source. 

Any insight here? Also, any idea which one is more accurate? Im hoping the forerunner readings :slight_smile:

Thank you!!