Differences between test rides

[aeropod.user]

Hello,

today I rode several test rides to test different configurations of my cockpit. Every ride was about 3km long - 1,5km out, turn 180 degrees and 1,5km back. The way out I perceived as headwind ride, the way back felt like a tailwind ride. I had the same helmet, the same shoes, the same suit.

From the data shown on my Edge I drew conclusion that my configuration from the test 1 was the fastest one. After ~2h I returned to that initial configuration and rode the test again to confirm initial values. I did my best to keep my position the same and stable.

Surprisingly, in Isaac I see significant differences between both test rides, which I cannot explain. Isaac shows that CdA from the the first test ride was 0,222 for the out part, and 0,229 for the back part. For the final test test ride it shows respectively 0,214 for the out part and 0,201 for the back part. What surprises me even more is that although my velocities were quite similar between first and final tests (37,9kph vs 38,5kph for the out part and 46,6kph vs 46,3kph for the back part), first test ride required much less average power than the second one to achieve those velocities (274W vs 337W for the out part and 292W vs 315W for the back part). I cannot map those differences to CdA values from both test rides, as typically with higher CdA one needs more power to ride at given speed.

Weather conditions were very similar, calibration of the device was the same. Aeropod was on for all the test rides.

Can you please help me explain from where this difference might come?

Regards,
Bartosz

[Velocomp]

I am traveling (to Eurobike) but I will try to respond as soon as possible.

[Velocomp]

I looked briefly at your files.

The first file does not appear to be an out and back (elevation is not symmetrical).

Were these two rides done on different courses?