Power meter wonky?

Not talking about needing calibration, but sending wrong reading consistently. Like the calibration needs calibrating. Been riding for years, doing endurance MTB. I’ve always been a middle of the pack finisher. I came back in August from a 20 month lay off from injury. First time training with power and a structured plan. My FTB is really low. 125 and that is up from 118 about 6 weeks ago. I’m 6’ 152.

Even though I’ve never trained with power and done a FTP test before this, I was shocked at how low it is considering how I finish in races and riding with buddies who either have or claim to have much higher FTP. The other day at my local LBS I got on the floor model Kickr bike and I was spinning at a little over 200w and it felt nothing like(easier) the 200w on my H3 at home. I do understand the bike calibration may be off as well.

I guess other than my ego, It doesn’t really matter. The resistance is the resistance regardless of the number you put on it. Anyone ever heard of a faulty power meter like this? Is the power meter in an H3 or Kickr an actual power meter or some algorithm with cadence, resistance, etc…?

  • It is not a strain gauge based power meter, like we see in the likes of pedals, crank arms and spiders.

  • The Kickr & H3 use the “magic” of the electronics and the resistance unit to back-figure the power, as compared to actual power measurement tools in their factory. It uses the internal device RPM, not rider cadence, as part of that process.

Getting back to your main issue, have you successfully completed a spindown calibration in the Saris app?

Yes, several times. It seems consistent. I wonder if it could be off like an oven thermostat? It reads 375 but actually 425 and burning my cookies.

OK. There are a range of potential issues like actual power data problems, but also to include gearing in use, test methodology, riding environment (temp/humidity), rider position and likely more.

Without an actual power meter used in conjunction with the trainer for direct comparison, there are only guesses to be had.

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Thank you. Is there an ideal gear using the Saris spin down calibration?

No, the gearing is not related to the calibration process in any meaningful way. All that is needed is enough device speed (at the rear axle) to hit the desired speed target for the trainer/app. Once you attain that and coast, you are all done. Gearing does not matter other than the cadence you apply to get that rear wheel speed as required.

Gearing can matter related to actual riding performance, to include FTP testing. High / Mid / Low gearing can be used depending on the bike as well as the control mode applied to the trainer (ERG vs Resistance). ​This leads to the impact that the flywheel can have on the feel when using the trainer.

If you test one way, say low gearing / flywheel speed, riding in higher gearing may lead to different feel and even FTP test results. that is in light of just changing gearing on a single trainer. When you then hop onto a different device (especially one as different as a Kickr Bike), you can have different results.

Essentially, until you define all the variables (FTP test format used, gearing used, environmental conditions) and then match or contrast those the same variables in the alternate situation, you have too many unknowns to do any real evaluation.

At this point, without a separate power meter, you may be best to contact Saris if you have any question about it’s data. Maybe they can review your calibration data and give you some feedback.