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CDA Measurement on a long Course. What was happening?

Posted: Fri Aug 22, 2025 3:45 pm
by quantus
Hi,

today I made a real world test run in Profile 4 to get a better understanding.
2 times 20 Minutes with same setting at threshold power on the same out and back course, Lap 2 and Lap 4.

The rides were pretty consistent, some wind and light traffic.

The analyzed CDA are different to garmin data. What was happening?
Screenshot 2025-08-22 212657.png
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Screenshot 2025-08-22 212809.png
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Ride file is attached.
Sorry for my english. I am from Germany :D
Thx

Re: CDA Measurement on a long Course. What was happening?

Posted: Sun Aug 24, 2025 7:29 am
by Velocomp
It looks like you bumped (rotated) your AP around 51 minutes. CdA and watts went crazy afterwards.

Lap 2 and lap 4 were out-and-back laps, good for CdA testing.

VA analysis can overcome the error in the "bumped" lap.

Analyzed lap 2 CdA was 0.204
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Analyzed lap 4 CdA was 0.201 (analysis corrects for errors in rotated AP).
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So, you got good results despite the bumped AP.