How/when to incorporate new PM and understanding power discrepancies

So I’ve been using a gen 1 Kick’r (wheel off) since November 2015 and it has been a solid and reliable training tool since (other than the bearings wearing out). Last week I jumped on the black Friday sale that Stages had on their power meters and bought a single sided one for my Cannondale.

Tossed it on the other night (TQ’d to spec) and then decided I would run a little test last night during my TR workout. I ran TR through a PC as I’ve always done and connected the Stages to my Wahoo Bolt. I zero’d / calibrated everything before the workout and then started it.

Right off the bat I could tell it was reading low so after the warm up I re-zero’d the Stages. First interval 5 min @ 88%, still reading low. So I zero’d again before the next. Same thing. On the last interval I also tried using a bigger gear to get more flywheel speed going and also putting TR into resistance mode but neither had a different effect on the readings.

Now I know these two power meters are not going to read the same but I am seeing a difference of 16-40 average watts between 6 intervals. This is from analyzing the Strava files since the session from my Bolt didn’t upload to my calendar for some reason.

One thing I wanted to try but couldn’t during the workout was to turn off power smoothing on the Kick’r. Not sure what that would help though. So, onto my questions…

First, does this seem in line with what others notice as far as power differences?

Second, I planned on eventually using power match so I can use my trainer numbers in the ‘real world’ with this new PM but I think it is going to be hard to transition my perceived exertion to the lower reading PM after all these years of “knowing my numbers”. I thought about doing my next ramp test in a similar fashion like I mentioned above so I can have a good comparison of the numbers.

Here’s the averages for the intervals…

Stages / Kick’r
236 / 252
234 / 255
241 / 262
231 / 269
212 / 252
223 / 258

Any help is appreciated!

Totally different readings. The kickr is estimating your power, stages is measuring your power. Run out a quick ramp test to get a correct reading and carry on.

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  1. You mention several Zero Offsets for the Stages. When did you last do a spin down on the Kickr?

  2. Recognize the potential for leg power impalance since the Kickr actually covers both legs while the Stages does the left and doubles the value.

  3. Do you know if you upgraded the Kickr firmware and did the advanced spindowns to swap it from the strain gauge PM to the Resistance brake PM calculations?

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My last spin down on the Kickr was maybe a week or so ago. It has always had very consistent offset numbers and the bike hasn’t been off it nor has it been moved for at least a couple months. It’s on the latest firmware and I’m 99% sure I did the Advance spindown as I believe that is the only available option it gives me.

I understand the single leg theory. I assumed if anything my left leg might be the stronger of the two being left handed. I dunno lol.

Another wrench in this mess… I do not intend to use this PM on the trainer all the time as I’m going to swap it back and forth between my road bike and cx/gravel bike depending on weather. So there will definitely be times when I am back on the trainer without the PM. So that means my “new” ftp numbers will be null at those times.

Good info on the trainer.

In the case of not always having the PM inside, I’d tend to just use the Kickr for power all the time.

Easier to use one “ruler” inside and leave the other for outside. You can recheck the delta between the trainer and PM occasionally for reference.

But the common differences we get for our performance in and out is just another adder to the PM vs trainer.

That means some potentially discrepancies in TSS of course, but that is life with 2 or more PMs.

Yes - first generation Kickrs have a general trend towards reading high. They are great training tools but my FTP dropped nearly 40 watts when I went to a direct force power meter from the first gen kickr

Agree with @mcneese.chad that if you won’t always have access to the power meter indoors then you’re likely better off using the kickr.

I would strongly recommend you record a single ramp test with your head unit recording the power from the stages and trainer road recording power from the kickr. This will give you a nice solid comparison of the relative power curves of the two measuring devices.

If your gen 1 kickr is anything like mine was you’ll have an inflated indoor FTP and a depressingly lower one with a more accurate measuring device

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I agree with this thinking, thanks!

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I will most definitely do the “dual test”. Thanks!

Bummer about the 1st gen reading high, I feel like my whole life has been a lie! lol

I guess this is a good case for an outdoor ftp test once the weather is more favorable.

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I don’t think it is universal across those units, but definitely a trend

I knew mine was reading high because I’d done some riding with a powertap hub previously, I didn’t appreciate how high until I was able to get a power meter on board - but it hurt the ego even though I knew the numbers were inflated

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I wouldn’t just assume that your 1st gen Kickr reads high and it’s my experience that over time, both during the workout and over the years, the ergs readings change.

I’m using a Kickr Snap (wheel on) and did the Ramp Test yesterday using the Kickr’s Erg while simultaneously recording my Quarq PM to my Wahoo Bolt. I generally use powermatch for workouts, but powermatch for the ramp test in the past hasn’t perform well. In my case, the Kickr consistently under reported during the ramp test this time, meaning that I was pushing more watts then my Kickr was reporting. Traditionally my Kickr used to track very close with my PM or even over state my power, but over the last few months it has since gone astray. Below are the graphs the Kickr’s erg (blue) versus my Quarq PM (red) during my ramp test. I feel that doing periodic comparisons between your trainer and PM is the only way to truly know your offsets.

Compared to my Ramp Test back in July 2019 where the Kickr and Quarq PM tracked very closely:

Well did Perkins -1 tonight. Same test protocol as yesterday but this time I turned off power smoothing and did a spindown on the Kickr prior to the workout. I’ve always done spindowns after workouts when the trainer was up to temp, not sure why but I think I read somewhere a long time ago that was the best way. :man_shrugging: Also, Advance spindown is not an option anymore, not sure where it went.

Numbers were very close throughout the workout. So close I thought maybe my Bolt was picking up the Kickr instead of the Stages so I selected “forget sensor” under Kickr just to be sure. Sure enough everything was good and the workout felt normal. The average power for the 2hr ride was only 4 watts different with the Stages being higher.

I’m going to keep an eye on this but hope the problem is solved :crossed_fingers:t3:

You still need to do a spin down on a Kickr if you use your own power meter as the power source?

If you are using PowerMatch with a power meter, the spindown calibration for the trainer is optional. We’ve seen mentions that it may help the PowerMatch process perform better after a spindown, but also the exact opposite stated.

So you can do whatever suits you.

I’ve had opposite experience with my Stages PM and my Gen 2 Kickr (maybe it’s a Gen 1 v Gen 2 thing). My PM always provides higher numbers than the Kickr. I’ve been attributing that to loss of watts through the drivetrain, but that’s just speculation on my part.

1st mistake is buying a Stages single sided power meter. I have single sided on my MTB and Gravel bike with Easton/Race Face spindle power meter. I know for sure that I am at least 2.5% lower power from my left leg at anything higher than Base/Zone 2. The more tired I get or if I do Vo2 intervals and start to fade it gets worse. When I get the chance I’m going to swap both of them out for Quarq or Power2Max so I’m actually reading the correct amount of power. I wouldn’t recommend single sided to anyone unless you really know what you’re doing and don’t get too hung up on the minute differences of the numbers. I can tell when I’m in the correct zone so it doesn’t bug me too much but there has definitely been a few workouts outside where I’ve thought I was feeling crappy and then I did some analysis when I used to have Garmin Vector 3’s and found out that I’m always at minimum 2.5% lower on the left leg. That adds up to a 5% difference on what you’re actually seeing on your Garmin etc. That starts to make a big difference in the 300’s and up. 340 watts for a Vo2 interval is different than 350 depending on how long you’re holding it.
Anyway that’s my rant.

Edit: While you can compare a single sided PM to another PM I don’t think you can say one is “too high” or “too low”. The variance created by the single sided PM can be significant and I would almost always put my stock in the Kickr, Quarq, dual sided, or any other PM measuring both legs as being more accurate.

I remember thinking I was totally failing a 20 minute test about 5 years ago. I had a little bit of a niggly issue with my left knee and afterward I realized that I was pushing probably 20 more watts than my Garmin was actually reading due to the fact I was using a Stages.

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I’ve had a similar experience, my Gen 1 runs 10-20 watts high vs Stages/Pioneer/PowerTap… lower wattage is more accurate, higher is less.

I’ve considered upgrading for quite awhile but it seems like I’ll just keep using it until it dies.

Good luck

My 4iiii left sided power meter runs about 10 watts lower than my gen2 kickr. I haven’t gotten around to using DCRs tool to see the actual discrepancy across all wattage ranges.