Using Assioma pedals with Tacx Vortex trainer

I’m currently using a Tacx Vortex with TrainerRoad and recently purchased a set of Favero Assioma pedals. Have been using them for around three or four weeks now and have no complaints with them…very quick and easy set up and seems to be reliable (so far anyway).

Have a query though on optimal way to use with TrainerRoad workouts…i’ve been using Tacx Vortex without power meter pedals for around 9 months now and have been used to the steady nature of the power fluctuations (ie. when an interval kicks in, the trainer takes around 5 seconds to shift power from recovery power to interval power but when it gets there, the power is consistent and feels that way too…all I need to do is pedal).

However, when using the pedals with the Vortex, the power fluctuates up and down. My understanding is that the output power is coming from the force through the pedals and that the Vortex is reacting to that force and then adjusting the resistance in an attempt to keep the power within targeted power. Is that correct?

My issue is that sometimes my output power remains stuck above or below target power for long periods (upwards of 30s) of an interval resulting in average interval power being above or below target. Believe this is to do with small changes in cadence…can anyone confirm?

I wasn’t too concerned about this because I was of the view that this would even out over time and in any case it would be more realistic and in line with how power feels out on the road. However, i’m coming up to doing a ramp test again soon and starting to think that it may skew results below what i am capable of if the power is held below what the target power is supposed to be at each stage of the ramp test. Am I right in thinking this?

Or does anyone have any more optimal set ups?


The first thing to do is read about PowerMatch. That is the “new” element when you add a power meter to the mix. It adds complexity to the system. Some people like PowerMatch, others do not. Experience varies and I know that it can impact the overall experience when compared to a smart-controlled trainer on its own.

One thing to emphasize no matter your usage. When using ERG mode, make sure you ignore power and do not try to “chase the target”.

  • You must keep a steady cadence so the entire system can do its job of adjusting resistance to hit the target.
  • Focus to hold your desired cadence as consistent as possible, and ignore power.
  • By doing this, you keep the system more stable and will likely reduce the fluctuations in power.

So, I also have a Vortex and Assioma pedals. And while YMMV, here’s a few things I’ve noticed about mine:

  • If you get behind your target power, you are screwed. That is, sometimes when I am doing sweet spot intervals, and I’m outside the power window for the trainer things go bad. If the trainer can’t get to the target power in my given gear, it’s like it “stores” instructions to keep trying (for lack of a better term for it). I might go through an interval with a target of 280w and the trainer can only get me to 275, then the trainer holds me at 275 for the entire recovery period or at least a large portion of it. Not fun.
  • If you are in a good gear for the power, the interval tends to start high then ease down to the target power. My average tends to be 1-5 watts high at the end, but pretty close. But, mercifully, the recovery starts as expected.
  • There’s a pretty bad watt ceiling. I can’t really get mine to push much more than about 700, and that only for a few seconds. Not saying I’m some exceptional sprinter, but Spanish Needle can’t seem to hold me at the right power no matter the gear sometimes. This seems to get worse during the workout, but increasing cadence fluctuations could have something to do with that too.

Again, overall I’ve found my setup usable, if a little hard to get right sometimes. Maybe one of these days I’ll grab a fancy direct drive and be done with it, but for now it works.

I’ll also add that I did my ramp test in resistance mode and shifted.


Thanks for the replies guys.

So, the best (and only) way to counter this is to focus on maintaining steady cadence then? There’s no other solution that i’m missing out on that would make the power changes less volatile?

Also, is this specific to using the pedals with Vortex or is it better with other trainers?

I’m considering not using the pedals for the next ramp test just to make sure my results are accurate…good idea?

On possibility for your next ramp test might be to use the Vortex as you have done previously. And have the Assioma’s paired with your Garmin, but not with TR. When you are done with the ramp test, compare the results of that, with the best 1 minute power recorded on the Garmin. That way you will have results comparable historically, and also an idea of FTP as measured by the Assioma’s.

Back when I had a Vortex and a single sided Stages power meter I noticed exactly the same thing. Here’s the post i wrote at the time. Follow the link for some graphs:

The bottom line is that, even without power match, the Vortex was requiring too much power at the start of each interval.

As far as I know there’s nothing that you can do about it (other than buy a different trainer…).


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Personally, i would not worry about the smoothness of the graph and make the Assioma my primary power source for all workouts and tests going forward. I use the same setup as you and know it the graph looks messy compared to the smooth graph you get with virtual power. But, as long as you are hitting the targets for all intervals and the IF and/or TSS at the end of the workout matches what it was supposed to then i would not worry.

The benefit of using the pedals as primary power source is that you can then use them outside and have a consistent measurement of power. I have had the Assioma’s since March 2018 and setup a new season with them in TR and then a ramp test. i then used this result as my FTP going forward as the pedals are more consistent than virtual power.

I recently got Assioma pedals with my Kickr Core, and have had the same behavior. The power fluctuations (especially when I let my cadence vary) I expect to some degree, but it still feels weird to me that the resistance supplied by the trainer varies so much along with it while it tries to keep my power constant. My interval power consistently comes out 2-5% higher than the target power - I need to drop the intensity for all of my rides now.

Thats a great suggestion…will try this on next ramp test (next week) and report back!


Lengthy and long winded post…

So I did the ramp test again this week using the suggested set up of the Tacx Vortex connected to TrainerRoad app and the pedals connected to the Garmin head unit.

I got the following results for max one min power:

TrainerRoad (Tacx Vortex power source): 330W (link to Ramp test is below)

Garmin head unit (Assioma pedal power source): 355W

Couple of points…

  • Power as per the Vortex is 330W giving FTP of 248W (lower than current FTP of 254W). Frustratingly, on the last step up on the ramp test the Vortex didn’t adjust power and it almost felt like the wheel was slipping so I was stuck on 330W for 30s or so. This has happened me before on ramp tests (I’m not sure why, sometimes it works perfect, other times it just “stalls” on the last ramp up). Once it was clear that the power wasn’t adjusting, I quit the test because I know from experience that it wouldn’t change and thought there’s no point in wasting energy because it wouldn’t translate to a higher FTP value. I think if it had changed though that I would have been able to suffer for at least another minute at the next ramp up in power (345W) which would have gave me FTP of 259W

  • Power as per the Assiomas is 25W higher at 355W which is equal to a FTP of 266W

  • Any thoughts on what FTP I should go with for next training block? Given the Vortex “failed” on the last step up and I’m confident I would’ve done at least another minute at 345W, I’m thinking I should at least go with 259W for the next training block. Or is it better to go with the 266W per the Assioma’s? I’m thinking the 259W is better because all the workouts have historically been based off the Vortex power or is that the wrong way to think about it?

  • Because the Assioma power level is tracking c. 25W (or 8%) higher than the Vortex, does this mean that the power for any workouts using PowerMatch is done at the Assioma power level or the Vortex power level? ie. is my power actually 8% higher than the Vortex power if I use PowerMatch?