How's the CdA experimenting going with everyone?

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kq6up
Posts: 57
Joined: Sun Jan 13, 2019 9:58 pm

How's the CdA experimenting going with everyone?

Post by kq6up »

I am wondering how your CdA experiments going. I am just getting my AeroPod dialed in very carefully to make sure my data is repeatable enough to see subtle changes in equipment to come out of the noise. How is it going for the rest of you? I am finding weight measurement is EXTREMELY important as well as measuring your own Crr by going very slowly up a hill. I am also noticing measurements can drift as you sweat through a long ride. If you measure your total weight plus the bike correctly, you will not see variation as you ride over the rolling hills.

Regards,
Chris Maness
BillOsler
Posts: 116
Joined: Mon Apr 04, 2016 10:10 am

Re: How's the CdA experimenting going with everyone?

Post by BillOsler »

You are probably correct in your assessment regarding the importance of measuring weight and Crr but I would still question whether you will get sufficiently precise measurements to compare results from one day with results from another. It's hard to measure tire pressure accurately, there are variations in wind, the clothing may be different on different days, there may be subtle differences in body positioning, et cetera.
I have had only a little success getting valid measurements thus far and I don't see any hope for comparing measurements taken on different days so all of my measurements involve a comparison between two setups that differ in only one respect. I might ride once on the hoods and then in drops or I might ride with my road helmet then with my TT helmet. Or without a wheel cover vs with a wheel cover. I do not intend to compare this week's ride with last weeks ride. All comparisons are based on rides done the same day.
kq6up
Posts: 57
Joined: Sun Jan 13, 2019 9:58 pm

Re: How's the CdA experimenting going with everyone?

Post by kq6up »

I am thinking to get really good results, you would need to have a statistical ensemble of the wind scaling factor. Instead of doing one calibrating ride, do 5 and average the wind scaling factors. This should sort out all the gusts, and also give you a standard deviation that tells you how reliable your CdA data is. It would also be a great benefit to do these rides on a really flat course, so that undulations and delays in the unit processing these changes can be ruled out. The error in CdA should be very close to the error in the wind scaling factor on a flat course. I can't think of any other variable that would change over the course of a ride.

Regards,
Chris Maness
GooseRider
Posts: 58
Joined: Wed May 10, 2017 10:52 am

Re: How's the CdA experimenting going with everyone?

Post by GooseRider »

I am wondering about the Crr. On the Powerpod it was automatically adjusted to reflect road bumpiness. On my very smooth bike path I have multiple underpasses with rough surface, every time I pass one of those, my CdA seems to change and take a while to return. Also, up and down seems to matter in CdA measurements.

Wonder what precision is on each of the inputs. Power vs slope vs wind vs surface vs rolling resistance estimate. In some way you would think that downhill no pedaling would be most accurate since accuracy should then only depend on Aeropod calibration and its sensors. However, if the slope sensor is less accurate than my power meter, might be better off going as flat as possible.

Morten
kq6up
Posts: 57
Joined: Sun Jan 13, 2019 9:58 pm

Re: How's the CdA experimenting going with everyone?

Post by kq6up »

I would agree about the slope sensors. There maybe some lag involved. I say as flat as possible, and tempted to bust out my surveyor's transit :D

Regards,
Chris Maness
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