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

(Fernando Jimenez 5656) #181

Just my 2c

Trainerroad has had this feature for a while, but as another poster noted, it’s useless for short intervals, and it takes a bit to stabilize. Real shame because I really like their training plans.

PerfPro, however, has it down perfectly. I don’t know the algorithm, but it works really really REALLY well. Whatever they are doing, Zwift needs to replicate it because otherwise there’s no chance I’m switching

(Steve Wood (B)) #182

Hi All - to those who use Kickr do you have the Wahoo app ‘control resistance with Power meter’ ERG option set to Off or On?


Does this option conflict with Zwift in any way?

(A rider) #183

Steve your question is not clear. Are you talking about using the Wahoo app exclusively?

(Steve Wood (B)) #184

hi - In the wahoo app, which I use to do Spindowns before workouts, there is also an option where you can put the Ant+ ID of your power meter in (Mine is a Rotor in Power at the crank). Wahoo says:

“The feature uses the power data from an ANT+ power meter to tune the KICKR’s resistance to match the power data of the power meter.”


So my question is, should I have anything in there if using Zwift? does Zwift override this or does it cause a conflict? I ask because I believe that even if the app isn’t being used (which I do not use once Zwift starts), the setting are committed to memory of the Kickr.



(Sunil Savkar WBR (C)) #185

I don’t think so.  When you route the ANT+ power meter through Wahoo KICKR, that is just used to re-transmit I had understood so that the KICKR is then reading the same as your power meter.

If you are using the new ERG mode which reads your power meter directly in Zwift, it should be using that data, not what is transmitted from the KICKR, for purposes of modifying resistance.

In any event, I use trainerroad in ERG mode where I always was using my pedals, and I also had the pedals (P1 pedals) connected up to the KICKR Snap as well when I was using previously with Zwift and I never changed anything.

But you should be able to figure this out really quick by doing some tests to see whether or not as your power meter shows different #s, is the resistance on the KICKR snap changing…

(A rider) #186

Watch Shane Miller’s video on this: 

He shows exactly how to do this.

Also, from BestBikeSplit:

Since the power reading from the P1 pedals and Zwift are consistently close, you can download the BBS plan as a Zwift file, load that to Zwift, and pair your Kickr as the power source and the controllable trainer and leave any head unit out of the loop completely.

If you want to use Trainerroad, you can download the Trainerroad specific file, and pair your pedals. Trainerroad has something called power match where they will use the power readings from the power meter to adjust the resistance of the trainer.

At any rate, loading the BBS plan or course to the actual headunit is probably the least preferred method to practice the race with a smart trainer in Zwift.

(Liam) #187

Hi guys

This feature is ace now it’s been fixed but does everyone else experience it yoyo 'ing around and taking a while to settle ?

It’s impossible (for example on Jon’s Short Mix) to go from 600w down to 100w (for one minute) and not fail the ‘rest’ interval. The power stays at previous highs for far too long

Is it using some moving average from my Stages crank?

(Steve Wood (B)) #188

I tried this yesterday on Jons short mix - I found that when it went to the 600w sections, the kickr basically locked up so much so i couldn’t turn the pedals - does anyone else get this?

(Liam) #189

TACX NEO worked ok for me… I could get a ‘perfect’ just couldn’t get a ‘perfect’ on the rest interval!

(Michael Henasey) #190

@Liam Hudson what do you mean by “This feature is ace now it’s been fixed?”

I gave up on Zwift’s “power match” and use TR instead. It simply works better in TR. I can live with running both.


(Liam) #191

@Michael Henasey… power match does work for me (largely) just doesn’t handle well (at all) quick changes in power output. For most structured training it works fine for me.

(Jim) #192

I know this feature is marked as ‘Completed,’ but I think that is an overly optimistic assessment. Like Steve Wood, above, I tried this on Jon’s Short Mix. My FTP is apparently about half of Steve’s, but I also found that when I hit the 300w sections, the Kickr basically locked up so much that I couldn’t turn the pedals.

Zwift: Can you please reopen this feature request and put a little more effort into it?

(Nigel ) #193

I did Jon’s Short mix a couple of weeks ago. There are 3 x 10 second intervals at 300% of FTP. For some people this would have the effect of locking up the back wheel. The problem is the workout with unrealistic power targets not ERG mode in Zwift. I use a power meter plus a Hammer smart trainer. I can’t do 300% of my FTP as that’s 927 watts for me. Around 800 for a few seconds is my limit.

All the workout is trying to do is make you go as hard as you can for 10 seconds. Once the 10 seconds is over you should be able to pedal again if you stopped.

(Jim) #194

My FTP is only 197 and the first high intensity segment is 295. I can do this segment in ERG mode if I use the Kickr as the power meter. I cannot do it if I use a separate power meter (Stages). Though the meters do read differently, they are not so far off as to make the difference between being able to do a segment or not.

“Power meter + Smart Trainer ERG mode” needs more work before it’s ready for prime time.

(Nigel ) #195

Suggest you file a support ticket with Zwift. ERG mode works fine for me using a 4iiii crank power meter and a Hammer smart trainer. If others were having issues with ERG mode not working I’m sure the Zwift Riders Facebook page would be full of people complaining. It isn’t.

Personally I find many of the zwift workouts have over optimistic power targets that are unacheiveable. I do Trainerroad workouts but using Zwift. These are much better thought out and acheiveable.

(Jim) #196

I have filed a support ticket with Zwift, but since their usual response is “be sure to post in the forums,” I thought I’d get a jump on the forum posting part.

For the record, I’m trying to use a Wahoo Kickr (2nd generation) and a Stages power meter, both connected to my Windows PC using the ZML/BLE hack. Perhaps that’s part of the problem?

(Nigel ) #197

How do you get on doing a workout without the super high short intervals? What I have read is that some people find their smart trainers can’t cope with very short intervals where there are sudden power changes as it takes longer for the trainer to settle down to the correct power than the duration of the interval itself. Then some take their trainer out of ERG mode for any workout with targets over their FTP (to avoid the spiral of death).

(A rider) #198

(Nigel ) #199

Rapid Pulse - What a load of crap and some terrible advice. The problem is almost certainly your Snap. I’ve been through 2 Snaps so have some experience with them.

The first lot of Snaps had problems with power accuracy. If you did the advanced spindown on an ios device you might have been lucky to get it calibrated correctly. Android users like me seldom got it to calibrate properly. The effect was that power accuracy was way off what my power meter was reporting e.g.

150 watts on Snap = 130 watts on power meter

180 watts on Snap = 180 watts on power meter

200 watts on Snap = 240 watts on power meter

250 watts on Snap = 350 watts on power meter

300 watts on Snap = back wheel lock up.

Now when you use ERG mode on Zwift with your power meter controlling the Snap if you have an interval at FTP or higher the trainer will first go to what it thinks is the right power. It’s then a back and forth process between the power meter and trainer as the trainer settles down to the correct power. This can take over a minute and the higher the target the longer the settling down process. For example Trainerroad that I also use adjusts the power every 10 seconds and only by 5 watts at a time. I assume Zwift is similar. So if your power target is 250 watts and the Snap makes you work at 350 watts it takes 200 seconds to settle down to the correct power.

So for ERG mode to work properly your Smart trainer needs to have reasonably accurate power even when using a power meter to control it.

I’m running a new power meter that reports power the same as the old one. ERG mode on my Cycleops Hammer works great even on intervals over FTP. Where I find it doesn’t work too well is 120% intervals of 3 minutes or more that I can’t sustain. I start tiring at 2 and half minutes and if you don’t keep on top of the power you get the dreaded spiral of death where your cadence drops and the resistance gets harder and harder. For these it’s best to do the workout in standard mode where you can keep doing the interval but let your power drop as you tire.

So anyone saying ERG mode doesn’t work should get in touch with their trainer manufacturer. Something isn’t right. In my case Wahoo said my power meter was at fault. I didn’t buy this and I knew of others with exactly the same problem. I’m now very happy with the Hammer and new model power meter (power on new power meter same as old power meter).

(Michael Henasey) #200

ERG mode with high wattage for a short duration is something I totally avoid.

ERG is great for longer duration intervals at a set wattage. For really high intensity stuff, just stick with free riding, change gears, and get those bursts in. Don’t rely on ERG for that. I put a free-ride block into my workout for sections I know Zwift and my trainer (a KICKR) will not be able to handle.

If you keep expecting Zwift or any app/trainer to be able to go from 200w to 800w for 10 sec, you will always be disappointed. The technology today just isn’t capable of doing that.

If you ask why there is a workout in Zwift that prescribes exactly that type of high intensity interval, it’s simply because Zwift copied some coaches canned workout into it. Unfortunately no app/trainer can actually handle such a workout. So yea, it really shouldn’t be in Zwift.

Just my 2c.