Tacx Neo power issue?

Have been using Tacx Neo 1 on zwift for a few years and recently bought a set of Assioma Duo pedals. When comparing power reading between both the Neo is usually 2-5% lower (which I’m putting down to drivechain) except on descents with high speed/cadence and low resistence where the difference is up to 20%. Has anyone else had a similar issue? I’m wondering if the Neo underestimates power on descents and pedals are more accurate, especially as they are brand new. Any thoughts would be appreciated.

Neo is hard work.

Are the pedals less accurate than the Neo?

It’s becoming increasingly common for people to question the neo compared to the Assioma pedals.

Makes me wonder if those pedals are a little unreliable.


I’d say the Assiomas are as good as and possibly more accurate than the Neo (2T). Both are rated +/- 1% for accuracy.

I was in the rather unfortunate situation of having to replace a Neo 2T under warranty. My original unit typically read around 6-8% lower than my Assiomas and my replacement unit now typically reads around 1-2% lower (direct comparison using the same ERG-based workout).

Gear choice (cross-chaining) can also have a marked effect on the relative power of the Neo versus Assiomas as the drivetrain losses vary.

Might I suggest to the OP that he repeats the same descent using a much bigger gear and a lower cadence (higher resistance). I bet the power difference is much less than 20% in this case?

Maybe this is why Zwift recommends doing ERG-based workouts using the small ring? I know from experience with my Neo that if I use the big ring and the workout calls for a low wattage, high cadence interval (e.g. part of the warm-up preceding the 2x20’ FTP w/o) the trainer has a hard time nailing the target power and it “hunts” up and down quite a lot.

1 Like

Thanks for the replies. Will be doing erg mode workout later in week to compare, though on free ride neo is slightly lower than Duos which id expect due to drive chain loss. Real issue is with high cadence/lower resistence when pedals read about 20% abive Neo. Hopefully its a Neo issue, especially if its becoming increasingly common for people to question Neo vs Duos. Surely if its the pedals it would be seen with other PMs and not just Neo.

There are a lot of possible failure points for power-meter pedals. (note: I own a pair of Garmin Rally XC200 dual-sensing pedals)

  • They need to be installed to a specific torque;
  • A hanging weight calibration should be done;
  • “Reset Install Angles” as part of setup;
  • Ensure crank length is correctly set;
  • Calibration while at a consistent temperature.

I understand the Assioma are supposed to have a simplified installation (just give the hex-wrench a couple of ugga-duggas, no specific torque) and then do a manual calibration.

However, I’m always more skeptical of power-meter pedals than the NEO line of trainers. I’d start by going through the initial setup process again - reset install angle, set crank length, do a few hard sprints to settle the pedals in, THEN perform a manual calibration.

TBH, I don’t think there’s an issue. The OP stated, “When comparing power reading between both the Neo is usually 2-5% lower (which I’m putting down to drivechain) except on descents with high speed/cadence and low resistence where the difference is up to 20%”.

If the Neo-Assiomas difference is only 2-5% when compared under “ideal” conditions (e.g. ERG mode in small ring, middle sprocket on cassette) then I think the 20% discrepancy is simply due to the limitations of the trainer when operating at high speed/cadence and low resistance.

Should be easy enough to check with a few ERG-based workouts under different conditions.

1 Like

I wonder if the neo’s downhill simulation is affecting things here where it spins the flywheel on downhills to simulate the negative gradient - maybe try it with the power off (which means this wont happen but everything else will work) to see if it makes a difference?

Thanks for the reply. Tried a coupme of erg mode rides and while Neo track pedals well, with a few % difference in favour of pedal. Once power and resistance drop, this difference increases. Also noticed there are rew spikes in power recorded from pedals, which is replicated in Neo, just not to the same wattage. Im putting this down to pedals responding quicker and picking up random power spikes that drop before trainer has fully caught up.

Orher that the lower power/resistance difference, every other time the difference is 2-5%. I just cant work.out which is off, or is it just me?

If the Assiomas are reading 2-5% higher than the Neo then that’s correct (relatively). Whether either of the two values is accurate is a different matter.

The question you need to ask yourself is, does it really matter?

So on dong some research it seems that high difference between Neo and Duos at lower wattages is a known Neo issue. Apparently if you’re in a higher gear, big ring small cog, the Neo has problems recording lower wattages and its more accurate in small ring bigger cog for lower watts. On reading this i repeated the ERG mode workout on small rimg and the difference between Neo and pedals dropped to about 5% on lower power and remained 2-3% on higher power. Just glad its not pedal issue.

1 Like