PP in MTB check

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kdx200
Posts: 171
Joined: Sat Jan 14, 2017 10:09 am

PP in MTB check

Post by kdx200 »

Hi John,

please see the attached to correct or confirm the setup.

did OB and its seems to be ok. I think sometimes underestimate the power..specially in flats.... going slighty up in the streets seems to be ok.

MTB 26x2.25 2,7 bar
handlebar locked
70kg me
12kg bike
1,75 height

i dont know if the parameters are ok. Long time ago with me TT bike i did some corrections you helped me in Isaac ... now i dont know where in the menu is this " arrow meter graph" to do the fine tuning.

thank you very much.
ale
Attachments
iBike_04_13_2019_0724_51_km_HiDef.ibr
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Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: PP in MTB check

Post by Velocomp »

Your CdA for the mountain bike position is too low. It should be around 0.433; the attached profile will fix it.

I'm also suspicious that your wind scaling is low, causing apparent constant tail wind. I changed it, but please do a short out and back ride, and post it for further checking.

Corrected ride file and profile attached.
Attachments
kdx200.ibp
(505 Bytes) Downloaded 180 times
kdx_04_13_2019_0724_51_km_HiDef.ibr
(1.19 MiB) Downloaded 177 times
John Hamann
kdx200
Posts: 171
Joined: Sat Jan 14, 2017 10:09 am

Re: PP in MTB check

Post by kdx200 »

Thank you... with this corrections seems to be ok as my efforts.

Doing a new OB is clicking the 4 second PP button protocol?

Thank you
Ale
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: PP in MTB check

Post by Velocomp »

Sorry, I was unclear.

Do NOT do a new calibration ride.

Instead, just ride your bike in one direction for at least five minutes, then turn around and ride back. Please post that ride file.
John Hamann
kdx200
Posts: 171
Joined: Sat Jan 14, 2017 10:09 am

Re: PP in MTB check

Post by kdx200 »

John,
here is a new ride. i think the numbers are ok with my feelings. Tell me you thoughts.

ALSO, at about km45 i entered in some heavy terrain...mud, little stones in bed format with about 2 inch deep, grass loaded with more mud and more little rocks (like the ones in train path)....obviously the speed went down and my effort was higher that the previous kilometers... and the power numbers ? went down dramatically. Then when i quit this zone the numbers went ok again.
Please teach my about this.. i cant understand the low-power numbers in that terrain.

thank you very much!!
iBike_04_28_2019_0737_51_km_HiDef.ibr
(1.06 MiB) Downloaded 154 times
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: PP in MTB check

Post by Velocomp »

Your ride file looks fine. Calibrations are correct.

One of the parameters you set in PowerPod is the rolling resistance (Crr) of your bike/tires. For your mountain bike, the Crr is 0.0087 (visible in Isaac stats window). This Crr rolling resistance value remains constant throughout the entire ride.

At KM 45, where you went into mud and rocks, your speed dropped because of the extra rolling resistance of the loose terrain; that is, Crr increased substantially above 0.0087. However, PowerPod has no way of "knowing" your rolling resistance changed because of riding into mud etc.

So, what happened is that PowerPod under-reported your watts in this section, because your real-life Crr is above the fixed 0.0087 value used in the calculations.

Just for fun, I used this command, to estimate the rolling resistance in the section in question.
Screen Shot 2019-04-28 at 1.56.22 PM.png
Screen Shot 2019-04-28 at 1.56.22 PM.png (172.29 KiB) Viewed 3575 times
I assumed your watts were about the same in the mud section as elsewhere (198W). So, by experimenting I determined the value of Crr rolling resistance that would increase your mud watts to about 198W. The value is about 0.03--about 3x higher than the lower rolling resistance elsewhere. This means that the rolling resistance in the mud section is much more difficult to bike through--which is what your body told you the entire time! :D
John Hamann
kdx200
Posts: 171
Joined: Sat Jan 14, 2017 10:09 am

Re: PP in MTB check

Post by kdx200 »

John, very clear. Thank you.

So, my heartbeats were rising in this section... can i supose that i was pulling "more" watts than the 198w?

Thanks again.
Velocomp
Velocomp CEO
Posts: 7793
Joined: Fri Jan 11, 2008 8:43 am

Re: PP in MTB check

Post by Velocomp »

kdx200 wrote: Sun Apr 28, 2019 5:54 pm John, very clear. Thank you.

So, my heartbeats were rising in this section... can i supose that i was pulling "more" watts than the 198w?

Thanks again.
That would be a good assumption. You were working really hard!
John Hamann
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