Control Wahoo KICKR resistance with Stages Power Meter


(Bogdan Urma) #1

Hi,

I use a Stages power meter when cycling outdoors. My Wahoo KICKR’s power is off and not by a constant amount either. I know this is all relative, but it would be nice if Zwift could find a way to allow the Stages power meter to control the Wahoo KICKR’s resistance. I also use TrainerRoad for example, and they implemented just this (not just for Stages, but in general) feature, which is outstanding, as my power inside and outside match. See this link: http://support.trainerroad.com/hc/en-us/articles/204631294-PowerMatch-Using-Power-Meters-with-Electronic-Trainers

Does Zwift plan on doing something similar? That would be a great feature to have. 

Thanks!


(Stewart G teamWBR) #2

I am sure you can do this just now. I use a Computrainer and control it with my Stages pm. On the pairing screen select the Stages for the pm source then your Kickr on the lower right window. Should give you a consistent power reading.


(Bogdan Urma) #3

Thanks - interesting. I tried that and although closer by a lot, there are still small differences.

I had my Stages broadcast via ANT+ to my Garmin EDGE 1000 for both power and cadence and the same to my Mac with ANT+ dongle running Zwift. Although the Wahoo KICKR was connected as a smart trainer in the lower right window, I’m not sure it was broadcasting anything - just being controlled by the Stages PM I guess. So why would the power numbers not be identical? Both from Stages and both ANT+. Just trying to understand why there are ANY variances. But thanks, it seems to work.

Can anyone from the Zwift team chime in and confirm that it should work this way and perhaps answer why the small differences? 

As I was saying, I also use TrainerRoad and the numbers there are identical. Same setup as described above.

 


(Bogdan Urma) #4

(Stewart G teamWBR) #5

I know what you mean. I can get better sprint power on Zwift through the Stages compared to through the CT on it’s own. It is still not totally the same either though. On a recent sprint my Stages had my max at 1295W yet the same sprint on Zwift was 1239W. Both using Stages data with one recording direct to my Garmin and the other through Zwift. I am not sure why there should be any difference. Maybe a different recording time, 1, 3 or 5 seconds?


(Eric C. (Zwift HQ)) #6

Each power meter/smart trainer will transmit slightly different levels of power - most of the time the +/- % will be so small as to not be that big of a deal. All Zwift does is read the data from the power meter and use that - we don’t modify those numbers at all.

For example, Stages only calculates power from your left crank and then doubles it while something like the PowerTap pulls power for both sides but from the rear hub. Every company has a different way of determining power - even crank-based ones will have variance between, say, the SRM and the Quarq.


(Bogdan Urma) #7

Hi Eric. So I take it that indeed Zwift is indeed programmed to allow an external power meter to be able to control a smart trainer’s resistance then? Just want to be 100% sure that my Wahoo’s power is ignored when looking at my power output. I’m confused as to your post as it does not answer my original question (or confirm it). 

Reading your post it would seem that is not the case because you talk about how different power meters determine power. What I was saying is why would ONE power meter differ in what it displays to two different ANT+ receivers. But that would be a moot point if Zwift doesn’t have the real feature I asked about. 

Can you please clarify?


(Eric C. (Zwift HQ)) #8

Hi Bogdan,

I think there’s a mix-up in the language being used here: Zwift controls the Smart Trainer’s resistance based on the grades on our course. A power meter does not control it at all.

You can use a power meter to transmit wattage data which Zwift will use to calculate your speed in-game.

So you can use Stages for power and, say, a KICKR to adjust resistance. But the only commonality there is Zwift. I suppose since the Stages will determine your speed in-game it indirectly controls the KICKR.


(Bogdan Urma) #9

Hi Eric,

OK, but does Zwift plan on maybe allowing for an external PM to control to KICKR’s resistance (per my original question)? As the Wahoo is all over the place and drifts, and as people use different PM outdoors, Wahoo itself has implemented a feature (as has TrainerRoad - see my link) that allows one to choose if the Wahoo KICKR’s resistance is controlled by the PM or not. If one choose to, then the power will match what they are used to outdoors - not 20w higher or lower or whatever may be.

The second question is if Zwift can at least read and record the power from an external PM and ignore the Wahoo KICKR’s, then why are the watts shown not matching what I’m seeing from that same power meter on my Garmin? In other words, Stages should show the same watts on Zwift as it does on my Garmin, no? If again I pair my Stages to Zwift along my KICKR, according to you, Zwift should show Stages watts, correct? So why even a small difference from what I’m seeing on my Garmin? 


(Eric C. (Zwift HQ)) #10

I think what you’re asking for is essentially what we are providing - ZWIFT acts the intermediary since you are riding in Zwift - we control the KICKR and the Stages provides the power.

As for why your Garmin is showing different power than Zwift, I can’t answer as I don’t know how Garmin or TrainerRoad chooses to show power.


(Bogdan Urma) #11

OK on the first, was a bit confusing, but it seems Zwift is ignoring the power from the smart trainer if one chooses to also pair a power meter, correct? In other words, if both a power meter and a smart trainer are paired, Zwift will only read power from the power meter. If the KICKR is paired as both the power meter and smart trainer, then obviously it would get the power readings from it. But otherwise power meter takes precedence, yes? If so, good :slight_smile:

On the second point, I thought ANT+ was a standard, so if my Stages is sending ANT+ data/watts to the Zwift app and to any other device, once every second, then in theory they should be the same, no? Thanks again!


(Eric C. (Zwift HQ)) #12

Yup - when we use another power meter for power, we ignore the data from the smart trainer (whether it be KICKR, Powerbeam Pro, Computrainer, etc…) - we give you the option to decide which device to use.

As for the second point: this is correct. In theory I imagine they should be the same. I wonder if the difference is merely in how they are displaying on screen? Are the numbers between the Garmin and Zwift WAY off (like 50 watts)? 


(Bogdan Urma) #13

Got it! Cool! That’s the way to go as it’s nice to know that 1 watt inside = 1 watt outside (using same power meter) AND have resistance control (smart trainer) but ignoring its watts as they will differ.

On the second part, I did a very short test today and looked at the data afterwards on TrainingPeaks. The differences were small, but still there. Max watts was where the biggest difference was don’t recall how much. I will do a longer 45min-1hour ride tomorrow and post back the numbers.


(Eric C. (Zwift HQ)) #14

Thanks Bogdan. If there is a difference that is small, it could be how we are displaying the numbers. I will have to double-check with the development team but I know we don’t display every number immediately, otherwise your wattage will be illegible :slight_smile:


(K.C. Race3R) #15

fWIW my Stages and Wahoo Kickr have literally perfectly equal wattage output. Granted they are both new, but they synch perfecttly, to a watt.


(Chris Heng) #16

im not so sure but i think the approach taken by zwift in controlling the smart trainers’ resistance based on the course profile is more logical viable in a sense that the resistance could be timed perfectly in relation to changes in the course profile/ gradient.

Imagine if the resistance is controlled by the power reading from the power meter, if youre just coasting up a hill, the resistance would match your effort or lack of it which may not be realistic in the real world.

The concept of resistance matching power is closer to the concept of classic or dumb fluid trainers i.e. the harder you go, the higher the resistance become without taking into consideration other factors such as gradient. If that’s the case then I don’t see the need for a smart trainer in Zwift’s environment.


(Chris Heng) #17

Having said that TR uses power match as TR is about structured training, not racing simulation and speed is not a concern. You will need the resistance to correspond to the intervals consistently, otherwise i would imagine spinning out of gear when doing i.e. sprint intervals.

In fact i believe TR is best used with classic fluid trainers and a power meter on the bike.

 


(Bogdan Urma) #18

What about now, when Zwift has implemented structured training and FTP and all of this? It gets tricky and will be all over the place…

Eric?


(Pete Kreishman) #19

I know this is an old thread but it doesn’t look like one answer was posted. You can set up the KICKR to be controlled by an ANT+ power meter. Go into the Wahoo Fitness App, pick the KICKR under sensors, turn on “control with ANT+ power meter” and enter the ANT ID of the power meter. You can also choose “get candence from ANT+.” That takes care of it. Then just pair with the Kickr for power source, controllable trainer, and cadence.


(M C) #20

In my experience, the power matching by KICKR firmware isn’t as reliable as that done for example by TrainerRoad’s OSX and PC applications, and trainers like the Neo don’t have any power matching built in. So, for a TrainerRoad user who cares about accuracy during structured workouts, the power matching built into TrainerRoad is an important feature.

From my trial rides in ZWIFT, it seems that it allows displaying power numbers from a connected dedicated power meter while using a controllable trainer during normal riding, but if I then switch to workout mode, it will only go into ERG mode if the dedicated power meter is disconnected and the controllable trainer serves as the power source, thereby relying on the accuracy of the trainer which is known to be way below that of a dedicated power meter.

Is this correct? Are there any plans by the ZWIFT team to implement power matching in workout mode? Knowing how it will evolve from the current functionality would help TrainerRoad users like me decide whether/when to switch.