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Vector 3 Accuracy Issues

MAGNUS_tm
over 6 years ago
I'm on my third set of pedals now, and while I no longer have 'disconnection' or 'right pedal sensor' missing issues, I'm seeing a consistent discrepency between my pedals and Kicks 17'.

My first set of pedals regularly measured 4-7% lower than the Kickr. The second set measured much closer to the trainer however it was plagued with spikes and dropouts issues much more so than my first set of pedals. As such, I ended up getting them replaced within a week.

Now on my third set of pedals and they are consistently 6-7% higher than my trainer. These too suffered a number of drop outs and spikes but that has since been resolved with the new battery caps. Still, the consistent variance is there. I've tried a number of things including following Product Advisory instructions previously provided by Garmin, calibrating before each ride, spin down on the Kickr (both regular and advanced), as well as recording in either Ant+ or BLE.

I previously had the Vector 2 and they were always within spec (e.g. 1-2%) without fail. Given my experience thus far with the Vector 3's I'm lead to believe the issue is with the pedals and not the trainer.

Can anyone suggest anything else I can try to get these to better line up?
  • 0 over 6 years ago
    Higher than the trainer is already better than lower. Bicycle drivetrain efficiency varies with power output. Your pedals need to measure higher than the trainer, because of drivetrain losses. I'll link to the source, if I can figure out how.

    "A number of researchers have studied bicycle drivetrain efficiency using test rigs in a laboratory setting where cadence, gearing and power could all be tightly controlled. The works of Wilson and Spicer are often quoted resources. Some of the findings which may be of real value to riders considering marginal gains have been:
    • Drivetrain efficiency of a modern bicycle (i.e. derailleur system with typical road gear range) peaks at about 98% in optimal conditions however variations of as much as 5% (down to 93%) are possible at realistic power outputs.
    • As power output increases efficiency increases because frictional losses become a smaller part of total input power. Typical best-case efficiency of a drivetrain in the 200 – 300 watt range is 96-97.5%. Above 300 watts typical best-case efficiency is 97-98%. Read on to understand what we mean by “best case”…"
    It keeps on going with detail: cross chaining, small cogs, high cadence, etc. all increase drivetrain losses. The Kickr just like every other device is also lossy of course and I don't know how Wahoo deals with that. Ultimately, if the Vector 3 pedals come in 3-5% higher, then they're probably spot on. Even your 6-7% differential could be accurate depeding where and how Wahoo measures.

    Source: https://www.cyclingpowerlab.com/Driv...fficiency.aspx
  • 0 over 6 years ago
    Ultimately it's hard to compare PM's directly against each other. Measuring at different points will give different results due to drivetrain losses as hansap has explained, you've also got a +/- 1 or 2% accuracy range (dependent on PM), if the PM's are at the opposite ends of that scale then you can also get a reasonable variance whilst still being within the accuracy tolerances.

    Having said that my Vector 2's, Tacx Neo and P2M all track very closely to each other. Certainly closely enough that I don't need to make any adjustments. Maybe try a static weight test on your Vectors or see if you can introduce another PM into that mix to give you another data point?
  • 0 over 6 years ago
    Higher than the trainer is already better than lower. Bicycle drivetrain efficiency varies with power output. Your pedals need to measure higher than the trainer, because of drivetrain losses. I'll link to the source, if I can figure out how.


    I'm aware and expect some drivetrain loss, however, in my experience I feel that 6-7 % is quite high. Especially when I've been able to more closely measure against the trainer with other pedals including a set of Vector 2 and Vector 3.... And keep in mind, my original set of Vector 3 pedals consistently measured lower than my trainer. I'm not sure I can chalk that up to battery cap issues.

    Ultimately it's hard to compare PM's directly against each other. Measuring at different points will give different results due to drivetrain losses as hansap has explained, you've also got a +/- 1 or 2% accuracy range (dependent on PM), if the PM's are at the opposite ends of that scale then you can also get a reasonable variance whilst still being within the accuracy tolerances.

    Maybe try a static weight test on your Vectors or see if you can introduce another PM into that mix to give you another data point?


    As I noted above, I expect some drivetrain loss, but the odds of being on the opposite ends of the accuracy range on both PM is a bit of a stretch... And I've been able to compare against other pedals (both Vector 2 and Vector 3)... I would like to do a static weight test though I've never done one, and from what I understand, I need a calibrated or certified weight in order to do so accurately.
  • 0 over 6 years ago
    As I noted above, I expect some drivetrain loss, but the odds of being on the opposite ends of the accuracy range on both PM is a bit of a stretch... And I've been able to compare against other pedals (both Vector 2 and Vector 3)... I would like to do a static weight test though I've never done one, and from what I understand, I need a calibrated or certified weight in order to do so accurately.


    Yes, you need a certified weight, so it's easy said than done to actually do. Another PM might be easier so you've got a 3rd data point.
  • 0 over 6 years ago
    You need a weight of known value, not necessarily a "certified" weight. If you can get a 25 pound barbell plate measured (to within 25 or 50 grams) at your local post office then that is accurate enough.

    ETA: If you do this, include the weight of any hardware you're going to use to hang the weight off the toe loop of the pedal.