Originally Posted by
dscohen
The MyWindsock app is supposed to give you some calculated coefficient of drag (CdA); however, you have to pay for the premium version of the app. It sounds like you might be able to make aero improvements to your setup and see those calculated in the app’s estimate. I wouldn’t have high hopes for its accuracy.
There are ways to improve the estimate but I don't think any current app (either free or paid) uses them fully. A couple of things that would improve usefulness is not just the estimate, but an estimate of the variability in the estimate; and a tunable time span across which to make the estimate. There's a bias-variance trade-off involved: longer spans tend to reduce variance but introduce bias; shorter spans tend to increase variance (which is why it'd be handy to have a way to assess that variance). All that said, we know that when conditions are right and the rider is being conscientious, on-bike drag can be estimated both accurately and precisely.