Wild Wattage Fluctuations

(Cody Wright) #1

Hi there,

I’m new to Zwift, using a Wahoo Kickr Snap and Wahoo Tickr connected via bluetooth (I’ve tried both via mobile app and directly connected to computer).

I tried doing the FTP test, and during the segments where it tells you to maintain a specific wattage, I noticed it was near impossible to complete each section successfully. The wattage would, by the second, fluctuate from around 60 watts to 299 watts. At first I thought it was due to some delay between hardware and software, but when I tried maintaining a steady cadence, the problem persisted.

Is this an “ERG mode” issue? Is there something I can try to smooth it out? 

(Jason K) #2

Fluctuating wattage is usually a sign your signal is dropping out. See our troubleshooting article here: https://support.zwift.com/hc/en-us/articles/115000111566-My-Bluetooth-signal-is-Dropping?section=201145295

Hope this helps!

(Graham Wright) #3

Sorry to hijack this but I am having the same issue although using Ant+ with a kickr Snap. Everything was working fine up until Tuesday (doing FTP builder) but now I’m constantly being told to increase power and then reduce power and so on. Nothing has changed in my setup at all and I don’t have any such problems with Trainerroad.

Incidentally I get the same issue if I use my power meter so it’s not the Kickr either. If it’s the same tomorrow I will be heading back to Traineroad full time. 

(Tazio Nuvolar (CLS)) #4

At what I perceive is a pretty stable speed, my wattage constantly fluctuates by 3-8 watts. Normal or is my speed sensor mis-aligned?  I have a wahoo blue sc on a lemond revolution.

(Cody Wright) #5

Basically I’ll be holding steady at, say 145 watts. Suddenly the watts will jump to say 190 (and if I’m in a workout it will yell at me to reduce power), then a few seconds later it will drop to say 80 (and the workout yells at me to increase power).

This all happens with no noticeable change in my cadence or output (meaning I’m not adjusting my riding style) and with no noticeable change in resistance on my smart trainer.

So basically I’m riding steady, my trainer is steady, but the wattage goes nuts. Does that help, Tazio?

(Tazio Nuvolar (CLS)) #6

After I thought about it, I went in and watched some riders’ power, and there seemed to be minor fluctuations on the order of what I’m seeing. I suspect that what I’m seeing on my rig is normal. I haven’t seen anything approaching what you are seeing. I’d say you should check the article Jason K referenced. Good luck.

(A Zmansbr) #7

Cody, did you ever resolve your issue? I’m having the same issue now.

I really doubt its sensor dropout given my setup.

(Nick Tsilas) #8

Also having the same issue on Tacx Neo. Any suggestions?

(A Zmansbr) #9

I switched to ANT+ FE-C to control my Kickr. Zwift and Wahoo support both say its due to various BT dropout but I’m not buying it. No interference in my setup, power flails on all devices via BT (MacBook Pro, iPad, iPhone, Android Phone, Apple TV). ANT+ finally got it somewhat stable.

(Karl Wallevik) #10

Same issue here; Tacx Neo. Tried to do an FTP-test, by the wattage fluctuates wildly - by as much as 100 watts - even though my cadence is steady. Impossible to settle into the right wattage - had to abort. 

(Andrew Pringle) #11

Same issue with new KICKR - think this is a Bluetooth issue but can’t find a fix about to send KICKR back - any help appreciated

(Arthur Lydiard) #12

Same here.  My speed and rpms will be stable (riding on a flat section), but my power fluctuates significantly (+/- 60 watts).  I use 3 second smoothing option on power, so the wattage fluctuation is ridiculous.   

I know it’s not my kickr as I just got mine newly recalibrated by Wahoo @ their facility.  I am using a windows PC, which means I have to use ant+. I’ve done all the troubleshooting recommended and my ant+ is within a few inches of the kickr.  I thought this problem might be fixable via bluetooth, but looks like those folks are having issues as well.  

Given how commonplace this issue seems to be, I would hope Zwift would prioritize coming up with a solution.  



(A Zmansbr) #13

Yeah this is kind of an annoying example of finger pointing between companies IMO.

I switched from BLT to ANT+ and it still wagged all over the place. Doing any workout that has power goals I still get only 1 or 2 stars. Have to focus super hard to pedal smoothly. I think the 3 second smoothing actually makes it harder to control because you don’t get feedback on your input until too late so you are constantly doing the wrong thing. The best way I found was to find a gear and RPM that equalled the requested power and just try to hold that. Still tough.

Then I bought a Garmin Vector 3S power meter pedal and set it to be the power meter (ANT+) and the KICKR as the controlled trainer and things work waaaaaay better. Still fluctuates, but not nearly as much.

I’ll note, that with the normal setup, power fluctuates differently on different days and different parts of the ride. I haveall sorts of theories… sampling frequency on PC/Mac, background processes eating CPU, KICKR not transmitting frequently (but this also is reported on Tacx Neo).

Zwift should publish their tolerances requirements for getting a star on a workout segment (maybe they have?). And they should give you credit for being equally above and below the target if they see your power all over the place with missing data.

(Arthur Lydiard) #14

So, I signed up for Trainer Road just to compare the wattage using Bluetooth vs ant+.  It appears that the power is very stable under TR which leads me to believe it’s a Zwift Windows Ant+ problem.  Hopefully, Zwift will get with the program and get BLE to work with Windows.    

(Tony Paahlsson) #15

Same problem here. I have a brand new Tacx Neo that I tried for the first time yesterday. Had to send a Tacx Flux back and bought this instead. Now I feel dissapointed because of the power fluctuations. The power reading of my former Flux was very stable compared to this. Even if I tried to keep a stable cadence on a flat road the power reading jumped around alot and some times in ascents when I knew I pressed hard the power reading was very low.

I hope that there is some fix to this problem.

Otherwise the Tacx Neo is fun to ride with the road feel and spinning wheel in descents.

(Markus Gramlich) #16


I am having the same problems with ANT+ and a Kickr.

Installed Wahoo Utilities App on my iPhone and with this app’s help I applied the latest firmware updates to the Kickr trainer, the cadence sensor. 

Then repeated the spin calibration 2 more times.

Wattage responsiveness has apparently improved. To be tested this week trying to accomplish defined training plans with peak work loads.

Will keep you posted.

(deborah nixon) #17

I’ve posted this question as well.  I also wonder if Zwift restricts power. I was doing an interval session with a group and when I did my 30 sec on I absolutely know my watts were climbing but not only did they not go past a certain point, for some seconds they went down a bit.  I was pedaling full out and harder than in the previous segments but watts didn’t go up.  Is there something in the algorithm that holds back wattage?

I do see pretty broad fluctuations at times- but not always. I know it’s not an ant+ problem or dropping of signal because everything else is fine inc cadence.  I believe it’s somewhere in the program but I have no idea where. It’s frustrating and causes me to wonder what my real #s are. I don’t have a power metre 

(David Williams) #18

So, I don’t think the question is “answered” by Zwift if there are 15 comments saying they have the same problem.  I also have this problem with Kickr.  The dropped Bluetooth link fixes did NOT resolve it. Zwift, please follow up.  Thanks. 


Hmm, wonder if a real person at Zwift looks at all the comments once a question is labeled as “answered” or only ones with key words that get flagged and escalated for response? So, here goes, #frustrating, trainer road is better, rouvy beats Zwift, demand my money back, class action lawsuit, Zwift is the worst.  Have a nice day, then. :wink:


(Michael B) #19

I’d also like to weigh in on this one. My power fluctuations are terrible. I’m training for the Prudential ride 100 and following the training plan but because of the wild fluctuations I pretty much fail every interval or section of the training plan. As others have said above, my avatar will also come to a standstill for a few seconds three or four times during the ride. I am pretty unhappy with the experience.

My set-up and process is: kickr snap, macbookPro connected to external acer monitor, monitor and power block is at a good distance away from the kickr, macbookpro powersource is also away from the kickr (but the same thing happens when it is just running off the battery), Ant+ dongle on extension cable right beside the kickr snap sensors, bluetooth turned off on macbook and any nearby mobile phones. I perform a warm-up and a spin-down on the kickr before the ride before attaching it to macbook and ant+

Am i missing something, expecting too much, is it a kickr Snap issue? Or should Zwift be taking more responsibility?

(Gerrie Delport) #20

Would you mind uploading your log file to www.zwiftalizer.com and post a picture of the results, this can possibly help to find your issue.