Use of DFPM data by iAero or Newton+

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Zoltan
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Use of DFPM data by iAero or Newton+

Post by Zoltan »

Sorry if it was already discussed, but does iBike consider that Powertap measures at the downstream of the chain, why the other DFPMs do not? I mean iBike can work the power data without considering any drivetrain efficieny, which is not the case with eg SRM.

I remember that there is some types of DFPM in Isaac, which can be assigned to DFPM as a sensor, but I never cared with it. Until now. Alas, I cant check this setting now.

If there is a distinction of PT from the others I guess there is a general coefficient like 0.97 or 0.98 to multiply power data of crank, pedal, chain and bottom bracket DFPM before calculating CdA by iBike.

Am I correct?
Velocomp
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Re: Use of DFPM data by iAero or Newton+

Post by Velocomp »

The iBike measures the forces opposing the forward motion of the bicycle.

The PT measures the torque at the rear wheel, that drive the bike forward.

For both the PT and the iBike, the forces applied by the cyclist to move the bike forward are greater than those measured at the rear wheel, or at the handlebars.

So, like the PT, we multiply the raw wattage measured by the iBike by 1.02, to account for the fact that the cyclist loses about 2% in the drivetrain; that is, the forces on the crank will be about 2% higher than those measured by the PT or by the iBike. 1.02 is the Cm factor that you will find in Isaac.
John Hamann
Zoltan
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Re: Use of DFPM data by iAero or Newton+

Post by Zoltan »

Thx for the explanation. So do you follow the opposite way that I assumed to make powers calculated by iBike and the DFPM comparable before getting continuous CdA with the help of a DFPM other than PT, do you?
Velocomp
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Re: Use of DFPM data by iAero or Newton+

Post by Velocomp »

Our readings are comparable to other DFPMs, no matter where they measure.
John Hamann
Zoltan
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Re: Use of DFPM data by iAero or Newton+

Post by Zoltan »

Velocomp wrote:... that is, the forces on the crank will be about 2% higher than those measured by the PT or by the iBike. 1.02 is the Cm factor that you will find in Isaac.
I forgot to mention that I have a PT Elite+, type is set to 5 next to ID of Power In and DFPM Model is set to PT ANT+ Sport. Now I feel I understood what there may be necessary to have these two data fields in Isaac.

Since I have a PT, I guess that Cm should be 1.00 in the profile, or also in this case should it be 1.02?

Anyway I will check tomorrow what it is in Isaac.
Zoltan
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Re: Use of DFPM data by iAero or Newton+

Post by Zoltan »

I checked and Cm is 1.02 even if I have a Powertap as a sensor paired to iAero. So now I am confused why to multiply the raw power data of my iBike by 1.02 instead of 1.00.
Davis6022
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Re: Use of DFPM data by iAero or Newton+

Post by Davis6022 »

Perhaps PowerTap also increases its raw data by 2% or so to be comparible to crank-based power meters which measure the direct power applied by the rider. Anyone know?
Zoltan
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Re: Use of DFPM data by iAero or Newton+

Post by Zoltan »

Davis6022 wrote:Perhaps PowerTap also increases its raw data by 2% or so to be comparible to crank-based power meters which measure the direct power applied by the rider. Anyone know?
I guess, it is just a glitch in that part of the software. I dont dare say that there is a mistake in the calculation of eg CdA relying on power data from PT, but definitely an error in displaying this value when PT is used and chosen in Isaac.
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