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Two footpods with same 935 don't match calibration factor and seem to report different speeds

I have a 935 and alternate two pairs of shoes for my runs.  Each pair was bought at the same time and has roughly the same mileage on them.  I have an ANT+ footpod dedicated to each pair of shoes.  I.E. each pair has its own footpod and that pod never leaves that pair.

Over the last few months, I've begun to suspect that the something is off between the two - sometimes I feel as if the indicated pace is higher or lower than my body is detecting.  Both devices are set, in the watch, to report speed always.  I dug deeper and examined the calibration factor, and indeed the actual calibration number is different between the two.  I have each of them set in the 935 to auto calibrate.

Anyone else seen this before?  I would think that the calibration factor is relevant to my stride and not manufacturing or hardware difference between two identical devices....i.e. I would expect each pod, if properly calibrated, to have the same exact #.  Is this a bad assumption?

I also can't seem to find a way to force calibrate with the 935 anymore - i thought that used to be an option but the only available option is auto calibrate.

  • I would think that the calibration factor is relevant to my stride

    No, it's relevant to the placement on the shoe. Make sure your footpods are tightly fitted and do not shift their position while running or between runs.

  • The calibration factor is different between each device and each shoe. Auto-calibrate is like "force" calibrate, since it will calibrate after each outdoor run. If you don't want to force calibration after each run you should turn auto-calibration off.

  • Ok, thanks - this makes sense to me.  Unfortunately it doesn't explain the behavior that I'm seeing.  They're both in the exact same position on identical(brand, model, size, mileage) pairs of shoes.  They never leave their locations.  The fit is nice and tight and they've never shifted that I've observed. 

  • Well, foot pods just aren't that accurate, and detected speed also depend on your pace, form, and cadence. Btw you shouldn't use speed always unless you have the Stryd foot pod, and if you do have the Stryd foot pod you shouldn't use auto-calibration.

  • I've had a similar experience over recent months. I'm not sure when it changed, but the pace from my footpod has been steady but off by a considerable amount, causing me to run faster than I should or just feel disappointed in my pace until I save the run and find out it was fine!

    I've tried with auto calibration on and off, but not found either that great. Maybe I haven't found the correct manual calibration value. 

    I'd been using the pod for 18 months with no issue so suspect it may be related to firmware changes since you are reporting similar behaviour. Recent updates have talked about changes to treadmill calibration and I wonder if that affects the ANT+ footpod since that was historically what you needed if you ran on the treadmill.