Did my cycling power really increase this winter on my Wahoo Kickr? Power accuracy and thermal drift on my Kickr

Do you train using a Wahoo Kickr that is in your garage or in a colder area like me?
I probably bought one of the first Wahoo Kickr’s in 2014 and was a beta user on Zwift. The Kickr is awesome and has brought me a lot of joy except …. for the finicky power readings who tend to deviate, sometimes substantially (30 to 50W) from my crank Quarq power meter. When I got my Kickr, I even got the mechanical calibration kit but all seemed ok. Then I got into Zwift group rides and races and forgot about the power discrepancy reported by my Kickr.

This winter, however, I decided to adopt the Zwift 12-13 week FTP builder protocol. To start I did the Zwift 20min power test with my Kickr controlling the resistance in Zwift. I know my FTP falls in winter and when testing indoor, yet I was so happily surprised: this was my first 20min indoor test during which I wasn’t dying or thinking of giving up AND the numbers were better than expected.
That is: the numbers reported by the Kickr power meter. Unfortunately, my Quarq reported quite different numbers (see Fig 1).


Note that Zwift uses erg mode except during the 20min test, which finished at about 2800s after which I rode some more in non-erg mode. I also show the OLS regression lines during the 20min test to show the slopes: I was “negative splitting” so that I could increase power near the end—as was evident by HR upward drift and last min power surge. The key is that the power recorded by my Kickr was 1) way higher initially (up to 50-60W) and 2) drifting down even though the 20min test started after 40min warmup on my Kickr while 3) the Kickr was NOT in erg mode and 4) I was negative splitting (hence riding harder as time progressed during the 20min as the Quarq regression line and heart rate line shows). Let me explain why, but first

I emailed Wahoo:

I probably bought one of the first Kickr’s. This weekend I did an FTP test and had a bike with Quarq power on the Kickr. After the recommended 10′ warmup I did advanced spin down, also calibrated my Quarq, and started the 45′ Zwift FTP protocol. My quarq was showing 220W, Kickr power showed 290W! I can live with 5% variance (total claimed accuracy of both meters) but 70W/220W = 30%… And I redid this with another bike that has another Quarq power meter with same results. What do you suggest?

Wahoo was sorry to read this and recommended I 1) shouldn’t do a regular advanced spin down; 2) clean the optical sensor on the Kickr and 3) use the Quarq in Zwift to control the Kickr resistance. I did 1 and 2, but I want to be able to use any bike (without a crank power meter) on the Kickr, so investigated further.

I emailed back:

I have been investigating this and notice that the Wahoo Kickr power meter watt numbers fall as the Kickr warms up—but it takes longer than 1hr for them to stabilize (and not the typical 10min). Is that because my Kickr is in my sunroom, which gets fairly cold in winter, so it starts at cold ambient temp ? (I live in Chicago and our sun room is only half heated and separate from rest of heated house. Inside wall temp is perhaps 55, but my Kickr is closer to outside window so colder.
Is there no temp compensation algorithm in my Kickr1, or anything to compensate?

The response was:

“suggestion would be to do a twenty minute warm up, then do the spin down on the KICKR and calibration on the power meter at the same time. The developer believes that this will help pin point which power meter is drifting. Though the KICKR regression is going down, the Quarq is seeing an upwards trend when both should be effectively straight lines if you are doing an ERQ workout.”

[The latter sentence is incorrect as the 20min test is NOT in erg mode. And even if erg mode were on, if there is temp drift during warmup while the Kickr power drives Zwift to control resistance, the resistance control changes over time (as the Kickr power reading drifts down) and effectively I have to start pushing harder. So, one would never see straight lines if there is drift.]
Anyway, I did 1) go back to the strain gauge for power measurement in the Kickr and 2) follow the spin down suggestions and did one after 30min on both Kickr (and Quarq) and another after 60min, reported on Fig 2:


I emailed:

I did what you suggested: 30min in did spindown and also Quarq power meter calibration. Repeated after 60min. As you can see in the graph, the thermal drift remains; it takes about 1hr for MY Kickr to converge to true power reporting.

My two graphs now provide “convincing (or at least reasonable) empirical evidence” that my (I emphasize: my Kickr; I probably bought one of the first ones sold) is strongly temperate-warm-up dependent.

Is there a fix/update for my Kickr? (even if it includes a new temp sensor or PCB board? Being an electrical engineer, this problem is not surprising and is simple to solve with a simple correction feedback control).

The response was nice (as always: thank you Wahoo) but left me a little disappointed:

We could potential replace the PCB for the unit, however both the technician and developers feel that it would not fix your power discrepancy issue. Another solutions they is a full repair/refurbishment. However the repair/refurb process will mean that you will end up with a replacement unit of near equal age. So if the issue is related to how the PCB thermometer for the 2014 KICKR is handling the temperatures of your room, then any replacement unit will likely have the same problem. The suggestion that both the head technician and developer feel is likely to solve this issue is moving the unit to warmer location in your house.

It really shouldn’t be that hard to have effective temperature control (negative feedback control loop) on the Kickr to compensate for ambient temperature that is cold (say 40F) given that the internal Kickr seems to need to converge to about 75-85F (who rides indoor at 80F?) for accurate power reporting. And it’s sad that if there’s an issue with the first version of the Kickr, that that issue “couldn’t” be fixed: surely, suggesting in Feb 2018 to sell me the same PCB of an old, refurbished 2014 Kickr with same lack of temp adjustment won’t solve the problem. I teach service operations and root cause problem solving to my MBA students and while the service communication has been wonderful, the root cause of this problem remains as of today…

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27 Responses to Did my cycling power really increase this winter on my Wahoo Kickr? Power accuracy and thermal drift on my Kickr

  1. It used to be quite common on Zwift for KICKR users to be flying with their free “KICKR watts.” They were almost up there with the zPower fliers, haha! It’s a shame such an expensive piece of equipment doesn’t just work out of the box. I guess first gen KICKR users were beta testers as the newer models seem to operate much better.

  2. Matt Atterbury says:

    I have a similar vintage Kickr and see similar results (though not measured to anything like this degree of accuracy).
    OTOH, it is great that when I do a Zwift race I am “kicking ass” (that is, hanging on!) to start with but then as others fade my Kickr reports more realistic power and I manage to mostly keep hanging on 🙂

  3. Brad says:

    Awesome description. This is exactly what i’m experiencing with my Kickr and coincidentally i also have a Quarq crank based power meter. I’ve also checked it against my 4iii which is consistent with your findings as well.
    I’ve had much the same response from Wahoo but my Kickr is still under Warranty so i’m requesting a replacement or repairs (but not holding my breath).

    Thanks for posting this information as it has been really helpful. I don’t suppose you ever had it resolved ?

  4. Ryan says:

    Great summary. I have been having the same issue with my kickr. Got the same response from wahoo. I find that in the middle of winter it is much worse and can take 40-50 mins to warm up. Spring probably only 25mins but still longer than you would expect. I now use my Garmin vector 3 to report power to zwift. I also have a really early model of the kickr.

    • Thanks Ryan. Yes, too bad Wahoo doesn’t have a simple fix (just swap the PCB inside so we get temperature compensation—as a EE, it’s not that hard to put a little temperature control circuit in there and I’m surprised they didn’t do that from the start…). Meanwhile, I will also start using my Quarq to report power.

  5. Ben Cureton says:

    Just changed my PCB but still get a huge power spike at around 30min. Really disappointing!

    • Ben Cureton says:

      Hi, I have my 2017 kickr in my living room only 4 or 5 meters from wireless point and not in any direct sunlight. It’s probably around 15-18c in the room most recently. I don’t put the heating on as I cook when I train.
      They tell me that my temp readings seem normal after the PCB change and it’s likely to be signal loss. It seems too coincidental that the resistance drops around the same time as before (35-45min).
      I can manually bump the risitdnece back up but then my power reading can be as high as 700w when I know I’m pushing around 300w.


      • So you experience a power spike (loss of resistance) around 35-45min consistently? And not temperature/warm-up related? (Does the 2017 Kickr have temp compensation logic in the PCB?)

  6. Ben Cureton says:

    Hi, just tried everything they suggested once more. Turned off all other devices, electronics and anything else I could think of before starting. At 50min I was sitting on a constant output of ~250w and then the resistance dropped completely off. I manually increased the resistance to roughly the same level and was then producing 700w.
    Reset and did a spin down to see if it would correct. It took 25.3sec and gave a temp reading of 273c.
    I don’t know about the temp compensation logic. My father is an avionics engineer so I might ask him to get to poke around and take a look.
    Wahoo seem very polite but are unwilling to accept there is an issue.

  7. Clayton Edge says:

    Folks – something to try here. Around this time each year as the temperature drops – and I start seeing the power between my power meter and the watts reported by the kickr diverge. It’s been like that all November – and so as an experiment last week I brought the kickr into a warm room overnight, and rode it in the morning – and it was reporting perfectly again.

    I do a spin down every ride – 19 minutes in, but I very very rarely perform a factory spin down. So I did the factory spin down this morning and noticed two things:
    1. The first spin of the three seemed to be reporting speed correctly
    2. The second spin of the three seemed to be reporting speed correctly
    3. The third spin of the three was reporting about a third the actual speed (54×11 at about 110rpm was reporting 14mph).

    That gave me the big clue I needed.

    Now under warranty in the past I have gotten this corrected by WAHOO providing a new topcap – the piece where the infra red speed sensor sits and that fixed it – but this unit is now well out of warranty.

    So…I removed the top cap (undo the two allen key bolts), and got a some clean tissue and cleaned the little black IR transceiver lens. There was no obvious condensation or oil on the lens that I could see. Either way though bingo, everything reported correctly again. The factory spin down worked perfectly, and the power on the power meter and the kickr itself were once again aligned.

    Might be worth a try, it takes two minutes to do.

    • Clayton Edge says:

      Should mention as well that I think it’s more to do with the condensation – the relative humidity in the room rather than temperature drift!

      • Thanks Clayton. Interesting hypothesis about condensation! (I had also cleaned the speed sensor but if it were the speed sensor, its accuracy would not change over 1hour warmup; i.e., it would not be temperature-dependent and hence would have the same problem when warm. Given that that’s not the case, your condensation hypothesis gains credence: it may very well be that at cold temperature there is a little film/condensation which gradually disappears as the flywheel spins and braking slowly warms up the flywheel and the unit! So the test here would be to clean the sensor at the beginning of the ride and see whether that changes the power reading.

  8. Hans Morefield says:

    John, I’m having, and have had for a while, the same issue with my original KickR now that it is in my (cold) garage again. The power meter is so off, I’ve reverted to using it like a dumb trainer and just measuring my HR and training accordingly.

    I’m thinking of buying a new KickR, but unsure if they (or other smart trainer) will have the same issue with cold temps. Any thoughts? Thanks, Hans

    • Hans: I’ve been using my Quarq power meter (on my crankset) to drive/control the Wahoo Kickr and that works great. Of course, that requires your bike has a power meter, but even if it doesn’t perhaps look into buying a used one? Would be cheaper than buying a new Kickr. [I would expect that Wahoo has worked on temperature compensation since the first generation of Kickr, but I don’t know.]

  9. I guess this explains why I’m so much weaker after getting a 2018 Kickr and replacing my first gen one and why I’d fail so many workouts on my first gen kickr towards the end. I’m still going to hook up my power meter and see if my 2018 is off, which I never did before because I didn’t want to put my nice bike on the trainer but the difference in perceived difficulty between my old and new Kickr is kind of drastic.

  10. Andy says:

    Have you upgraded the firmware so it’s using the new mode of measuring power?

    • I upgraded last year before I did the test. Used both the brake-measurement and the old measurement. Didn’t make a difference. Or is there a more recent firmware upgrade that could alleviate temp-drifting for first generation Kickrs?

  11. Frantz Weitemeyer says:

    My kickr gen 1 suffers exactly from the same issue.
    During Spring, cyckling in my shed, I got stronger and stronger until I realized that something was not right. Temperature dropped over a month and a half from 20degree celsius to 5 degree, what a difference.
    Wahoo couldnt do anything for me, ended up bringing that noisy machine inside our home again.
    My Kickr is very sensetive to temperature changes starting even a few degree coulder than normal temperature is visible, and takes a really long time to varm it up.
    I dont see the reverse effect from higher temperatures.

  12. Angus Wragg says:

    Jan, thanks so much for posting this. Wish I had found it before – it confirms long held suspicions.
    I too have a near original kickr and have noticed this in the cold (mine is in the garage). Have been Zwifting more of late and find my rate of perceived exertion increases for similar measured wattages over time. Seems to take a full 45 minutes to warm up.

    Which means my ‘training’ isn’t as ‘efficient’ as it should be……

  13. Bill Slobotski says:

    Found this thread while researching my 2014 Kickr. Wahoo’s directions for a spindown is to ride for 10 minutes before doing the spindown. I took this 10 minutes to be a minimum number, so after doing some wicked workouts lasting an hour I did the spindown. Later in the season I did an FTP test and it was a HUGE increase. I doubted the result. So I contacted Wahoo about calibration and spindown issues.

    Their reply to me was NOT to do a spindown after a long ride because the accuracy of their calculations will be off. And yet Jan Van Mieghem is showing just the opposite – the Kickr is more accurate after an hour. So what to believe! My inner electrical engineer is bothered by this.

    • Bill: I’m also an electrical engineer so trust the data :). Now, there is no contradiction: my data shows that the 2014 Kickr power meter becomes accurate after quite some time (if it is in a colder area). This is independent of the spin down (which should be some calibration and, of course, it matters when you calibrate: what my data shows is that the 2014 Kickr has no good temperature compensation control). So don’t trust your 2014 Kickr watts—I put a bike on with an in-crank Quarq power meter and use that power meter to drive Zwift.

      • Bill Slobotski says:

        Sorry, I didn’t word my phrase “So what to believe!” properly. Your data definitely proves that the longer one rides the more accurate the Kickr. I am just kind of confused and sad that maybe all the increases I thought I had made are just because of bad circuit design or bad modeling of the spindown. Maybe I’ll get some power cranks at some point.

        On the topic of firmware – I wonder if your test was done with the latest firmware v1.5.68 . I honestly dont remember when this version of firmware was released – 3 years ago? Last year??. And even more honestly, did not realize *until this week* that at some level of firmware they eliminated the strain gauge. If your test was done with a version previous to 1.5.68, perhaps in the later versions they upgraded their temperature compensation routines?????

        Also, I notice in your Fig 2 graph that the Kickr starts to be more inaccurate on the low end at 5000 seconds. I wonder if this inaccuracy will continue to grow with time? Feel free to do a two hour ride and report back 🙂 . (I honestly dont know how anyone can sit on a trainer for 2 hours. I am a Sufferfest addict and shake my head when I read about people who reach Knighthood – 10 workouts in a row. WTF.)

      • I had the up to date firmware—see my response to Andy on 1/31/2019

  14. Kim Juul says:

    I have been having a somewhat similar issue with my kickr and driving myself crazy trying to figure out what is going on. I was riding zwift in my house on my kickr and had no issues. My husband build a room in the garage with a portable a/c unit for our bikes. We live in South Texas. It is almost always hot and humid. The a/c only runs right before and during our rides. I noticed a significant decrease in my power even though I am pushing as hard or harder. I tried all kinds of trouble shooting. My husband put his bike with a power meter on my kickr and it shows around 13% lower watts than his power meter, which is the difference I have been seeing in my numbers. I’m not sure how to solve this problem since the bike now lives in the garage. Maybe I can wipe the sensor and that will help. I think our issue must be the humidity

    • Bill Slobotski says:

      I was reminded of this thread after getting notification of Kim Juul’s post.

      This last spring I bought a new Kickr 18 and sold the Kickr 14 . And wow, the new Kickr 18 is ***** A LOT ***** harder to pedal. I do The Sufferfest and usually a warkout’s warmup power is 120-140 watts. In my Kickr 14 I could turn the pedals at 140 without even trying. On the Kickr 18 I feel like I need a warmup to the warmup because 120-140 gets my heart going.

      My ego took a huge hit! My FTP dropped about 20% from the 14 to the 18.

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