Stages (L) vs Hammer H3 - Which can I trust?

Hello experts!

Greetings from Sweden! Any friendly power guru out there with some advise? What equipment do I trust and how can I feel confident in the accuracy?

I have a Hammer H3 trainer, and a left sided Stages Ultegra crank. These are now reporting quite different numbers. Comparing the rides for the past 2 weeks, my impression is that the Stages reads around 10% lower than the Hammer H3; persisting through calibration/zero offset on both units and a hard reset of the Stages. Meaning 200W on TR is around 180 on the Stages, 300W is around 270W and so on.

Here’s a comparison between Hammer H3/TR and Stages/Garmin530 on my ramp test today (don’t mind beyond the ramp as the Garmin recording time spent vehemently panting):

My power training history is:
Wahoo Kickr Snap in October 2018 (wildly inaccurate, tightened until no wheel slip but comparing to the Stages power could differ ±80W even between consecutive calibrations)
Stages (L) in April 2020
Elite Turno in August 2020
Hammer H3 in October 2020

My impression in the autumn’20 was that both the Turno (hated the feel) and the H3 matched my Stages result (TR on a laptop, Stages on my Garmin). Having followed a training plan since October, I’m now checking in on the Stages power meter again so that I can ride within my ability outdoors.

Now this has me either confused or disappointed. During the past 6 month of training, I have seen a decent improvement in FTP (245 27-Oct, 249 today with high point of 257 at the end of Base). Burnt out a bit on mid volume halfway through Build and learnt my lesson. :smiley: But mostly I have been able to spend a lot more time in each Zone which has me excited to ride outside again and continue to work on my power.

Best 20m Power outdoors (though I never went full gas for 20m) was 216w, best effort on a TR ride (Galena -1) was 241w. Riding outdoors I ended last outside season averaging 31-32kmh on 40-80km rides, and perception wise it feels like I have pushed more watts indoors than outdoors.

As both devices seemingly are consistent, what would you do in my cycling shoes? I want to enjoy riding outdoors again but I also want to trust the numbers.

  • Carry on riding, recalculate my training zones, my left leg is probably just weaker?
  • Distrust either device as something might be off?
  • Invest in a new power meter for both legs (thinking Assioma’s or P2M) and use power match indoors instead?

I would prefer to avoid the third, I don’t print money for a living! But will bite the bullet for the best option.

Thanks to anyone who made it this far! :smiley: //Michael

My advice is to detach your ego from the actual numbers and just use your Stages to train by (indoors and outdoors). One power meter is the way to go so you can set your training zones. Going back and forth between two devices that are 20 watts apart will just give you bad data.

Believe me, I went through this and spent a lot of time on it. I got a Stages and couldn’t even come close to the wattage on my Tacx Vortex. The Tacx was 25-30 watts high on FTP and 70+ watts high on sprints.

I spent a lot of time testing and found that my Stages measured 5 watts higher than my PowerTap hub and 30 watts lower than my Tacx. It was very consistent. The Vortex is the wildly inaccurate device. I’ve since got a Kickr and it reads 10-15 watts higher than my Stages.

If I want to stroke my ego I can state my FTP in Kickr watts or Tacx watts but in the end it just doesn’t matter. It’s just a number from a device to train against.

(FWIW, I did a hard reset on my Stages and it helped a little. Watts came up a bit. It couldn’t hurt.


I made this topic when I was trying to figure out my Stages.

Neither. Get a Neo :stuck_out_tongue_winking_eye:. Pick one and go with it

Cheers for the reply! I did read your thread before which caused me to try the terminal short. :slight_smile: Seems like a very similar case.

You might be very right though. However I like to think I’m in it for optimal training rather than just a number. There’s plenty of tail wind segments out there to chase Strava KoMs with for that!

I had a very bad experience using the Kickr Snap two years back, which I believe is due to the inconsistent measurements. I performed a spin down before each workout but some workout just left me spent for days while some felt like a walk in the park. Only to go back out riding again in the spring and not seeing more benefits than I would probably get for ticking of hours based on HR Z2.

I just want to have something I believe is consistent. After all your investigation, did you find the Stages is consistent enough for you day to day and at different levels of fatigue?

What was your process and timing for calibrating the H3?

  • Hot or Cold, as in before any warm up or after some amount of warm up?

Usually complete the step up ramp in the TR workout then calibrate. Usually 10-15m into the workout. Some cases after the workout.

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OK, good. Not everyone does that, so you should be good in that sense.

On the question of what to trust, not sure anyone can answer that.

  • From the outside, I see a direct force power meter like the Stages to be more “consistent” since there is so little involved in the device. Strain gauge, temp sensor and some fancy circuits. In theory, something of a minimal design.
  • Compare that to the trainer which has a belt, pulleys, bearings and the sensors it is using to estimate power. It is not “measuring” power in the same way as a direct force power meter. It uses a different process that is subject to the friction in the entire system, as well as temp changes. There is far more to potentially impact the results than the Stages above. Theoretically, they have that all covered via the calibration, but I don’t know if that will be true forever and in all cases.

Without at least one more power meter to play between them, not sure you can really know which is “best”. Unless you are getting clearly “bad” data, you are likely best to pick one, be consistent with calibration and ignore the other.

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Yes, I think the Stages is very consistent.


I see this on my personal stages/ H3 as well. Since I use the Stages both indoors and out, I use it to guide my workouts. But when I brag to my friends about power PRs, I use the H3 numbers :wink:


Cheers for the replies, both. Helping it sink in that both devices probably are “good” just showing different numbers.

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I need to make a power meter meme for this, but essentially, this is true:

A man with a watch knows what time it is. A man with two watches is never sure.


Always use the power measuring device that gives you the highest number.

…kidding. I also have a Stages (Gen 3, Left) and use it both indoor (controlling a KICKR Snap) and outdoor. It’s extremely consistent, but I will say that I can do bigger numbers outdoor than indoor. I can’t say whether that has anything to do with ERG mode, the Stages controlling the trainer’s power or something else.

I haven’t bothered comparing the two because I know how obsessive I am, and if there was a known discrepancy it would drive me crazy more than it would help. Therefore, I just use the Stages and don’t bother checking it against the KICKR.

On a side note, when I bought my KICKR Snap I felt it was reading ~50w low, but I soldiered on with a bruised ego and accepted what many told me was reality. However, after doing a factory spindown and hard-reset of the KICKR it suddenly re-calibrated to read about 60w higher than what it was and my FTP felt like what I thought was a realistic number given my race history and competitiveness with peers.

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