Hub Torque vs. Crank Torque?

Discussion in 'Power Training' started by BillM, Sep 10, 2006.

  1. BillM

    BillM New Member

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    1. How does PTap even know crank torque...and

    2. What is the significance in the difference?

    Will this point to an inefficiency in the drivetrain? What is a normal variance between the two numbers?
     
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  2. frenchyge

    frenchyge New Member

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    It doesn't, power is calculated from hub torque and hub speed.

    PowerTaps read about 1-2% less power than the crank sensing SRM. Drivetrain efficiency is lower at higher cadences. There's little significance in the difference, IMO.
     
  3. jws

    jws New Member

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    1) CPS calculates crank torque via PT hub torque, speed and cadence.

    2) crank torque is hub torque times the gear ratio.

    drivetrain inefficiency will be ignored in the calc. by CPS since crank torque is merely back-calculated.
     
  4. BillM

    BillM New Member

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    Gotcha. I suspected as much...thanks for confirming.
     
  5. frenchyge

    frenchyge New Member

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    Cool, that must be new in WKO+. I'm not sure what that'd be used for, but maybe it'll be interesting when I start my iso-power intervals on the trainer this fall. Or wait... this is exactly what my SFR workouts have been lacking! ;)

    Certainly crank torque is more useful to have on the graph than hub torque, since it allows you to see the gear changes.
     
  6. Alex Simmons

    Alex Simmons Member

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    Useful for Quadrant Analysis
     
  7. frenchyge

    frenchyge New Member

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    Good point. Thanks. :)
     
  8. jetnjeff

    jetnjeff New Member

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    I am trying to Custom Periodic Chart to show Crank Torque for specific CPs 5 secons 3 minutes etc. But they all come out as Zero I know it is a calkculated number, but why have the option in Channel if all you get is zero?
     
  9. RapDaddyo

    RapDaddyo Active Member

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    Not to mention better data to confirm your 40% increase in power due to (secretly) using PowerCranks all winter.;)
     
  10. Lucy_Aspenwind

    Lucy_Aspenwind New Member

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    I'm detecting, and it is every so slight, a sense of sarcasm towards PowerCranks :rolleyes:
     
  11. RapDaddyo

    RapDaddyo Active Member

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    Who, me? Not a chance. The 40% improvement figure (I think I have that right) has been stated in promotional material about the PowerCranks. And, of course, I take promotional claims at face value, don't you?;)
     
  12. Squint

    Squint New Member

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    You know all the top pros are secretly riding with PowerCranks in their basements. Their outdoor training rides are just for show.

    Bags of blood and doping journals may have been uncovered by investigators but PowerCranks are kept even more secret. That's why a picture of a pro riding PCs is rarer than one of Sasquatch.
     
  13. Lucy_Aspenwind

    Lucy_Aspenwind New Member

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    Absolutely. Unquestionably so, to be more precise.

    Now excuse me while I go buy those little power insoles I have heard so much about - who needs a PT? :rolleyes:
     
  14. jws

    jws New Member

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    your cadence might not be working; if cadence is missing, cps can't calculate crank torque.

    after trying it myself, it doesn't work for me either, so maybe cps won't do it!
     
  15. jetnjeff

    jetnjeff New Member

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    Yeah I have Cadence recorded. Funny that Crank Torque would be available as a channel and not work. Bust be a bug.
     
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