Use Zwift Hub or Assioma Duo for Zwift Races?

Hey everyone,

I recently saw a hotly debated post about the question of which power source to use for racing - smart trainer or Assioma Duo. I use a Zwift Hub, but until very recently used my Assioma Duo as the power and cadence source as they are more accurate. Two weeks ago or so I switched to using the Zwift Hub as my power and cadence source and double-record my rides. For LIT workouts, the two are very similar. However, I noticed that for low-cadence workouts (at around 300-400W), the Zwift Hub usually reads 10-20W more than my Assioma Duo. Same for high-intensity intervals at higher cadences.

Here comes my question: I am new to Zwift racing; today I did my third race, the first one using the Zwift Hub as my power source. Again, it showed higher power than my Assioma (both the Hub and Assioma were calibrated before the race). The average W on the Zwift Hub was 314, whereas it was only 304 on my Assioma pedals. I am in cat B, so I guess no one really cares, but today I ended up on the podium for the first time and wondered whether I also would have made it had I used the more accurate Assioma pedals. What’s your opinion? What should I use for future races?

You can find the dual-recording data from today (24 Jan 2025) in which I used my Zwift Hub as my power source on my ZwiftPower profile (Jonas Grunau). Feel free to also check out the data from the DBR Zwift race on 8 Jan 2025 in which I used the Assioma pedals as my power source in case someone is interested in the context of sticky watts or something like this.

Can you see the data sets on ZwiftPower? I set visibility to public, but I’m new to this, so feel free to confirm you can see the data of the two races.

Looking forward to hearing your thoughts!

Assioma duos are some of the most accurate and well regarded power meters in the market. I’d use them.

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Okay thanks, interesting. People in the other thread seemed to strongly prefer using the trainer as the power source despite lower accuracy

Any ‘serious’’ or Elite racing would prefer/mandate trainer first - but any of the Elite racing series wouldn’t let you race on the hub as there is an approved trainer list knocking about.

The issue in the other thread was also the sticky watts and pedalling style…

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I only saw one dual recorded race.
My inexperienced opinion is that it looks ok.
Both power sources appeared roughly within 2-3 %.
The problem with Assioma’s is people can use an un natural pedal style that overestimates power.
You don’t seem to have done so.
Your trainer seems ok and your pedals seem ok as you are using them

I suggest to use the trainer, dual record and continue wearing a HRM.
I don’t see an issue but there are far more experienced and knowledgeable sources on the forums.

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First, congratulations on your performance really impressive numbers.

Reading from Zwift Cycling Esports Rules & Regs (not sure anyone cares about rules&regs) for Elites your primary device would be the trainer, the secondary power recording device (b sample) would be the pedals.

Back to your Zwift Power dual analysis results, if the Assioma’s have a zero offset/calibration process have you performed that? Thanks for sharing your data, it’s really good only +4% when sprinting.

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I was the person who triggered that heated discussion.

I have since purchased a Kickr v 6 and use that as primary source with the Assioma as secondary (although don’t always bother as they generally track the Kickr almost identically).

Problem with the pedals is that if you are really on your limit, desperately trying not to get dropped, you’ll likely find yourself veering chaotically between Z6 and Z1 in a world of pain. Then you might trigger sticky watts.

I would avoid this as there are some weirdos going around on a mission to expose sticky watt cheaters and the debate can get unpleasant.

Also, your trainer is giving you better watts than the pedals…just sayin’.

Well in this case the Duo are better here, Hub really give out bad number when Hot. @Casey_Schumm_X

I think that this is an exaggeration of what actually happens.
Failing rider tend not to rapidly and freq fluctuate between Z1 and Z6.
They may drop to Z2 and recover.

An E racer on the verge of getting dropped might resort to such an abnormal (and higher energy cost) pedal technique to hold on in a tight spot.

This pedal technique never happens IRL.

I also XC MTB and I am out of the saddle all the time but never start /stop at the frequency or the massive change between Z1&6 that we see in e racing.

I do not feel sticky watts is an accident because you have to work hard to do it.

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I’d have to work really hard to do it now, with a trainer that doesn’t enable them.

The powercurvers are pretty good, but it is hard to say one is more accurate than the other.
As for dual recordings, there are some “unusuals” that are easily spottet. Not much here, but if more it would be suspicious

Your pedal power rises more rapid when time → 0
That could indicate that crank length is set wrong

Your trainer har more 20m power
That could indicate that spindown is manipulated

If both manipulated, the curves would typically cross mid, in your case 1:10 minuttes but the average power on both would still be decent

I am not saying you have, and the variance is small, I am saying it is one of the factors (among others) you can spot it.

But…There will be differences. There shall be as power is measured in two different ways.

Here is one of my finest looking duals. I never get a total overlap like DC rainmaker and the likes, and I have 3 top shelf trainers and 6 crank based dual sided powermeters

This is BTW done in TPV with native dual recording

On your reading, the different sources has different power profiles

As for what to use?
Use the one you feel for, for most that would be the one with the highest reading
Trainers are usually more trusted as a source as pedals can easily be manipulated

Not quite, it’s certainly what I do when I run out of gear/s (more often on a singlespeed than a geared bike), one last push before starting to coast, then a few pushes again and more coasting etc.

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Sure, no doubt riders use everything but the issue is how long do you do so?

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Depends on how long the descent or strong tailwind section is…

Zwift Hub have heat move go bad when higher then 250 watts for 20 min, know bug with Hubs. @Sjuren Hubs are Very bad. if you go over 250 watts.

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Aaah…so it should really be moved to Zpower

No, but if i was you i would be looking at kick core next move. @Sjuren

When I see this pattern my initial assumption is that the Assioma’s have a lower crank length setting than is actual.

Trainer primary is generally the best approach because it reduces the number of ways that people can cheat. Some trainers can be exploited etc but it’s trivial to cheat with assioma.

Is it the pattern of initially reading higher then becoming negative?
I would assume the Assiomas should be higher than the trainer.
Mine is but I think it reads above at all time intervals.
I’ll check.

This was my race today.
My trainer was not as calibrated as I would have liked because I was distracted doing a climb portal and forgot to spin down till in the pen with 2 min to go.