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Is the accuracy of a pedal-based power meter (examples) significantly affected by using them with pedal extenders (example)?

Thank you.

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    Be careful, you won't be able to connect many of those pedals to those extenders. Only those that support external pedal wrench are possible, not any of those that require internal hex key. Dec 6, 2023 at 7:17
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    The strain-stress curve should still be valid. But I may be overlooking something, I normally work with fluids, not solids. Dec 6, 2023 at 7:19
  • @VladimirFГероямслава Thank you for the warning. My combination fits works physically and connects well to the head unit. I'm just concerned whether the readings are accurate.
    – Jim
    Dec 6, 2023 at 8:22
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    @DoNuT: I don’t see how bending the crankarm could cause a pedal based power meter to be less accurate. I’d also assume that you bend the crankarm much more when you are sprinting out of the saddle and pulling the bike left and right.
    – Michael
    Dec 6, 2023 at 11:52
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    Having an Assioma Uno pedal entitles me to contact their support since I can enter a valid pedal serial number in their contact form - I've asked them about extenders and will add this here if I get any response.
    – DoNuT
    Dec 6, 2023 at 17:36

1 Answer 1

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I've emailed Favero about this, but this reddit thread features a fairly recent answer from their helpdesk (11 days ago when I initially wrote this).

“As far as the Look version is concerned, we confirm you that Assioma UNO/DUO is used by many customers with pedal extenders up to 25mm without any issue. Talking with our technicians about this topic, they suggested to us that there are some extenders with the hole which could be the most suitable for the installation on the pedal (we remind you that you should not apply any force on the sensor to avoid damages).

Other comments there state that they haven't perceived any significant change in power. This doesn't rule out that it has a theoretical effect because it extends the lever on the spindle but I'm not enough of a physicist or mechanical engineer to understand what this could mean to power readings via strain gauges.

Here's what I got as response

Even if we are aware that some cyclists use pedal extenders, since we have not tested them directly in our facilities, I kindly inform you that we cannot guarantee their full compatibility and safety of use with Assioma. For this reason, I do not recommend using pedal extenders also because any possible damage to the product due to its incorrect use, may not be covered by the warranty.

I kept asking about impact on accuracy of their powermeters with extenders and got this:

As mentioned in my previous email, as far as I know, Favero Electronics never tested pedal extenders in our facilities but I confirm that we are aware that some customers use them, in particular the ones with the hole. Since they have never been assessed in our facilities, unfortunately, neither I nor our engineers can effectively confirm if the employment of pedal extenders could have any influence on the accuracy and/or display of the power readings.

To sum it up

  • It works for some riders based on user experience.
  • Favero as one of the well-known manufacturers of pedal acknowledges that these combinations work for some riders out there but haven't conducted any testing and would potentially deny warranty claims related to pedal damage when using extenders.

Verdict: Use at your own risk.

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    Thanks for updating. I feel like that isn't a great response from Favero - they could have asked their engineers if they had any theoretical concerns, or said that they would test the issue when able.
    – Weiwen Ng
    Dec 7, 2023 at 15:29
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    @WeiwenNg Yeah, answering this should be in an engineer's paygrade if you already developed a power-sensing pedal in the first place but they obviously don't want to open up that box for warranty reasons, even though somebody else responded in a more positive way. I could ask Shane Miller/GPLama on YouTube if he wants to run a test series about that...^^
    – DoNuT
    Dec 7, 2023 at 16:45
  • I don't know if pedal extenders would affect accuracy, but there are ways to measure accuracy. The "virtual elevation" method that's used to measure aerodynamic (and rolling) drag was originally developed as a way to check power meter accuracy.
    – R. Chung
    Dec 7, 2023 at 18:06
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    @R.Chung You could just put your bike on a smart trainer in ERG mode, run it for 15 minutes at a given nominal power and compare against the pedals on a head unit. Once with and once without extenders.
    – DoNuT
    Dec 7, 2023 at 19:14
  • @DoNuT There are two problems with that: first, you'd need a smart trainer with ERG mode; second, that would measure a difference (if any) between the two but it's not a measurement of accuracy.
    – R. Chung
    Dec 7, 2023 at 22:53

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