Hub Torque vs. Crank Torque?

BillM said:

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

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

BillM said:

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?

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.

BillM said:

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?

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.

jws said:

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.

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

jws said:

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

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.

frenchyge said:

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!

Useful for Quadrant Analysis

Alex Simmons said:

Useful for Quadrant Analysis

Good point. Thanks. 🙂

frenchyge said:

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.

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?

frenchyge said:

this is exactly what my SFR workouts have been lacking! 😉

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

RapDaddyo said:

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

I'm detecting, and it is every so slight, a sense of sarcasm towards PowerCranks 🙄

Lucy_Aspenwind said:

I'm detecting, and it is every so slight, a sense of sarcasm towards PowerCranks 🙄

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?😉

RapDaddyo said:

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

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.

RapDaddyo said:

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?😉

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? 🙄

jetnjeff said:

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?

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!

jws said:

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!

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