Control smart trainer's resistance with external power meter - important for Workout Mode

(Fernando Jimenez 5656) #61

E. Jackson

Consider yourself lucky then, or perhaps Wahoo are better at doing this than the rest. I know that the Kickr is one of the better units out there (although not sure about the Snap).

I also know that most smart trainers simply estimate the power based on the resistance applied and the RPMs of the roller. I reiterate, this is just an estimate, and there are too many variables in the equation for it to have any real accuracy (tyre choice, tyre pressure, how tight the wheel is pressed against the roller…)

In my case, my trainer reports about 50w extra when I’m doing 100w, and about 25w lower when I’m pushing 250w. Fine if you just want to pootle around Zwift, but not good if you want to do structured interval workouts.

Yes, of course you can use the trainer without Erg mode, but that defeats the purpose of a smart trainer in the first place. If I wanted to do that I’d dig my Kurt Kinetic out of the basement (solid unit that it is)

(Paul Holmgren KCK) #62

A lot of comments. 

Some I agree with some I don’t. 

Thanks Eric M for your answer. 

My personal opinion is. 

TrainerRoad implementation of “power match” is not perfect but it works for me. 

If Zwift was to implement a similar function as a intermediate solution until they solved the problem with the perfect “power match” between a power meter and a kickr I would drop TR and commit to Zwift. 

(Stewart ) #63

My trainer (Computrainer) also perfectly matches both Stages and P1 pedals so I can use Zwift’s ERG mode without any problem. I do still use TR as well though.

One thing I will say though is that TrainerRoad is a waste of time doing ERG workouts using power from the pm. Far too much lag so if Zwift were to make their’s the same then I don’t see the point.


(A rider) #64


(Fernando Jimenez 5656) #65

Hi E Jackson


I completely forgot about this until I spotted it today. Sorry about the one month delay!


IIRC, Wahoo was or has implemented a feature in their trainers where the trainer could read power values broadcast by a power meter, and use that to adjust resistance. Is that happening? if so, that could explain why your Snap seems to give accurate results. Otherwise, if power is computed as an estimate based on resistance applied at the roller, there’s little chance of any real accuracy there without using a good calibration protocol (and using it frequently). I’ve tried the calibration with my Vortex and no amount of attempts or swearing got me anywhere near accurate power readings


  1. Not sure you can say that when you don’t really know what kind of accuracy and consistency I’m looking for. PerfPro gives me exactly what I’m looking for, so it exists. Perhaps I haven’t explained myself properly. On the other hand, the experience in PerfPro is not comparable to Zwift, but it does work


  1. An individual’s setup is largely static, except things like tyre pressure, and often pressure of the roller against the wheel. Not sure how that is relevant though


  1. Not sure what your point is. Of course I could take the time to work out the error in the system, and adapt all my training plans to take these errors into account (assuming they are somewhat static). That would also mean I’d have to adapt the workouts in Zwift (not sure that is possible). But life is too short and it’s sunny outside :slight_smile:


  1. That is a very simplistic view on things. FTP is not just a number, it has a meaning behind it. Try holding your your 300 watts for an hour when you have an FTP of 250w and lets see how you fare. I suspect you’ll be dying in around five minutes


  1. Indeed! but some of us want to maximize the value we get out of our limited training time. But I’ve just about had it with the trainer until next winter, it’s getting nice outside :slight_smile:


  1. Awesome! that’s what we are all after, improvement! the only downside is that it gets harder and harder to earn it :frowning:




(Dany Geller WT RIO) #66

I changed to TrainerRoad while swift does not support erg mode workout reading power from my vector.

(Stewart ) #67

Danny, I have tried this myself but if you are doing shorter intervals TR seems to have a big lag making it not the best way when using pm power.

If you know the difference between your pm and trainer power numbers then you can use the TR offset and that allows you to avoid the lag issues by working through TR app.

(Dany Geller WT RIO) #68

Hi Stewart. The problem is that the offset is not constant along the range of power (100-180w). Maybe it’s a function of temperature, cadence, method of acquiring the power etc.

My workout’s interval are never less than 1 or 2 minutes. I get lags of 5 to 10 seconds ONLY to reach the power goal of my workout. I think it’s reasonable.

What is the software developing difficulty to swift accomplish this?
Or it’s a priority issue.

Nevertheless, I’m ok with TR Until zwift moves forward.

Thanks again!!

(Fernando Jimenez 5656) #69


I have the same problem. The only software I’ve found that does this correctly is Perf Pro, although I haven’t looked around in the last few months. Perhaps others have caught up by now



(A Simashin (B)) #70

some news on it? it is almost autumn again ) 

(Jorgen) #71

Really looking forward to this feature!

(Fernando Jimenez 5656) #72

Same here. Autumn is almost here, and soon I will retreat back into the pain cave, hence will be making my training choice for the winter

Zwift, any chance this feature will see the light of day for this winter season?

(William Fazackerley) #73

I use Todays Plan to set up my workouts. On there I have previously exported .ERG files out to my PerfPro Studio application which controls my turbo (Tacx Vortex) based on my power meter (Stages). This has worked well.

A month or so back a new ‘export’ feature appeared on the list; ‘Export to Zwift(beta)’.

I haven’t tried it as I no longer have a valid Zwift subscription (and I’m generally not training indoors at the moment) but I would be interested to see if anyone has used this and what it offers.

(Brandon Amos) #74

Its been five months since it was stated that this would be implemented.  Any further update on when we can except this to be working?

(A Simashin (B)) #75

Hi, subscribers of this feature request.

I`ve got some new from Eric on this, in strava - .

If somebody cant read it on strava ill post it here - 

Eric Min - It’s definitely on our radar. Our priority is iOS at the moment. We’ll come back to this afterwards but it would help if the community up-votes this feature so it gets priority over other features”


P.S. Thanks for reply Eric. Any info is way better, than silence

(Harry) #76


(anon51943766) #77

I’m not going to use zwift until this feature was enabled. Meanwhile I’m using perfPro

(A Simashin (B)) #78

One month more and this Feature request will have a second birthday (, seems it would not be done ever.

There are only 2 ways to solve this problem for now -

  1. is to buy more accurate trainer like NEO or Kickr2 and use them for workouts

  2. who haven`t money for NEO or Kickr2 the only way is continue(or start) to use TrainerRoad or perfPro - which include this feature.

P.S. By the way i know people which cant understand at all what is ERG, they do workouts without it. But i think if they ever tried it, theyll vote for this :wink:

(Greg Hilton ARCC) #79

another workaround is that I had my Garmin doing the controlling of power on the Kickr via it’s workout mode and had Zwift running to keep my interest 

(Mark Ponikvar) #80

For me the issue is that I don’t want a work around, I want it to just work.  I don’t mind doing work arounds for free software.  However, I have a large issue with paying a monthly fee for software that I have to do workarounds for.  Such a large issue with it, that I stop paying for the software until I don’t have to do workarounds.