Tacx NEO 2 power accuracy

Hi guys,

My Tacx NEO 2 shows lower power compared to Assioma duo power meter. I tested my FTP on Zwift, and the results were as below.

Tacx NEO 2: 190W

Assioma duo: 220W

It seems Tacx NEO 2 outputs 10% lower power constantly. Is there any way to fix this?

  • Hi, is it on the latest 0.0.36 firmware? Did You make zero offset calibration on your Assiomas before ride as always? How is the Zwift configured? Neo's power in Zwift and Assioma's power on a cycling head unit? Via ANT+ or BT? 

  • Firmware is not updated since the purchase. Assioma Duo was calibrated before the FTP test. Zwift power config is immediate, not 3 sec average. I use only ANT+. I tested twice on different days after rest.

    In addition to those FTP tests, Zwift paring view shows 10% watt difference between Tacx NEO 2 (ANT+) and Assioma Duo (ANT+).

  • okie, what is the actual firmware in the unit? Can You tell me? 0.0.31 or lower? pls update it to 0.0.36 with a reliable mobile phone, it helped on some N2 units in the past (the 0.0.34 already), lots of units had 20-25w offset issue

    The Zwift 's power smoothing is just a visual setting for the HUD, not for the recording interval (that is 1s always). 

    Did You set the Assiomas's crank length in the cycling head unit also (You need to set it in Assioma app and in the cycling head unit also otherwise the head unit will overwrite the app settings if these are different) , ok it cant cause 10-15% overmeasuring but it could be a source of small error.

    Do You have direct link for this comparison? (ZwiftPower dual chart or similar?)

  • I've updated the firmware from 0.0.18 to 0.0.36. Also I've just configured my crank length in Assioma app from 172.5mm to 170mm (Thanks for the info). However, I still see power difference like 190W vs 210W. I'll check further and make some charts to show the difference. 

  • okie, but set 170mm in your cycling head unit (if You record the Assioma power's with a cycling head unit), spin the cranks, the Assiomas are waking up and under sensor details (in Garmin head units) there will be crank length setting and the default is 172.5 for sure and need to modify it to 170 also (If You record the Assiomas's power with Zwift and the Neo's power with a head unit then the Assioma App crank length setting is enough) 

    What is the used gear ratio during these tests? small ring front and middle cog at rear? (36/19 for example or totally different or it was in SIM mode and variable gear ratios depending on terrain)

    How is your balance with Assiomas? 50-50? When You will do tests, pls do single leg drills with both legs (1min left leg, 1min both leg, 1min right leg, and do it 3times, @80-100w range, in ERG or in SIM, doesnt matter, and we will see the difference betwen Neo and one pedal and both pedals too)

    Okie, I'm curious about the charts! 

  • Here are the results. Tacx is constantly 5-10% lower than Assioma. ERG was off.



    I configured crank length for Wahoo Element Bolt in Wahoo Element app before those rides.

    My gear ratio is compact and 12t-25t.I normally use middle gears for rear, and I use both inner and outer for front depending on power.

    My left/right balance is not tested and I'm not sure how to see it in some app for now. I'll check it.

  • got it . Could You do the single leg drills also in these 2 comparisons? 
    I think You can check your balance postride in the Wahoo history log (in the Bolt or in the App maybe under details, should be an avg balance value for the entire workout). If You dont find it, share the fit file here (in ZIPped format) and i can read it out easily. 

  • Here is the result of my single leg drill. I did 1 min right, 30 sec rest, 1 min and 30 sec rest three times. Never did this kind of drills before, so it could be too messy to analyze...


    My left/right balance was 47/53 in last three rides.

  • for me it is ok :), yep, on right side your difference is bigger than with left leg as i see with this single leg drill, and if the balance value is 47/53 than your right pedal is measuring a bit more with a few % then it should (and if your right leg stronger in reality too then the stronger right leg with overmeasuring right pedal can cause higher difference when You are pedaling with 2 legs comparing to N2) . Can You get a 20kg dumbbell or similar? You can validate your pedals with this method: https://www.dcrainmaker.com/images/2018/08/Assioma-Static-Weight-Test.pdf   sometimes the factory slope calibration is not accurate and can cause over or underreport in the pedal . With this test You can check it easily as described.

    It is a very good drill btw , it can improve your pedaling fluidity. Question , is your saddle at ideal height? If You are unclipped, put your both heels to the pedal, can You pedal fluently backward or are your hips leaning left and right to get closer to the pedals otherwise You lose the contact with your heels? the too high saddle position can cause a bit overmeasuring too due to the streched position and the legs (muscle) will work against each other during the pedal stroke 

  • I did static weight tests for both pedals with 10kg weight. Both pedals measured the weight correctly. No left/right difference.

    My saddle height is supposed to be optimal because I did Shimano bike fitting a year ago. I'll try lower position and practice the single leg drill more Slight smile