Monitoring apparent CdA during a race

I raced sunday on a flat course during 2 hours with the CdACrr app on my bike (a criterium with 30 turns). It was the first time I recorded data during a race, and the post analysis is interesting. The first 5 laps were not recorded (I forgot to push the "start run" button), but we can seen clearly on each lap the influence of drafting. I spent 8 laps (lap 4 to 11) alone in front of the race, with the peloton just a dozen of seconds behind me. The CdA was stable and between 0.30 and 0.31. Before and after my escape the apparent CdA was oscillating between 0.24 and 0.27 (I was generally in the first five positions). I think I spent the whole 14th lap (CdA~0.215 in the middle of the peloton) and the lap 13th in the first position, hands on the hoods as nobody wanted to ride at this moment of the race. The second picture is the average power per lap (300-310W during laps 4 to 10) and 320W during the last lap where I chased behind 5 riders in the final. I remenber also that during the 23th lap, I was always in the second/third positions of the peloton (CdA~0.225).

Velodrome test

Field testing isn't easy. 

Lesson one: one turn (250 meters) per lap is enough to compute a CdA value. Adding more turns for a lap do not reduce variability.

Lesson two: the first turns should be systematically discarded.

Lesson three: keeping a constant position on the bike should be the goal number one.

1.0 Release

The CdaCrr app has been released this week on the Google Store.

For the moment, it has only been tested on Samsung S4/S5 and Sony Xperia Active phones and it records correctly from a PowerTap powermeter.

It implements Virtual Elevation method (aka: Chung method) to measure CdA (aerodynamic coefficient of drag) and Crr (rolling resistance coefficient) when riding a bike.