marcag wrote:
I am trying to understand how going lower impacts frontal aero
When the snow melts I will do this with field testing, but I am trying to understand the math behind frontal area, especially how much would I save for every cm drop, assuming I am starting from a position where my head is way above my back. I understand that there is a low point where you will get diminish returns.
In this article (http://www.endurancecorner.com/Alan_Couzens/bike_fit_4) the author claims “For an average 6ft tall cyclist, moving from a 73 degree seat angle to an 80 degree seat angle will decrease the frontal area by ~.03m^2,”. This is about a 10cm drop according to him. So let's say .003m^2 per cm.
I then put this .03m^2 in a power calculator and it says that if I reduce by .03m^2 I could save 15watts.
15 watts, 10cm, about 1.5 to 2watts per cm drop
Does this make sense ?
If I take the widest point of my shoulders when crouched/compacted is say 30cm * 1cm lower = .003m^2. Does this make sense?
Along with feild testing you can do some quick dirty work with a camera and a tripod set up about 20 feet in front of your bike on a trainer. Mount the camera lens at your chest level when you are in the aero position. Take the photo against a while wall behind you. Photoshop the image into black and white and "sort" the pixels. You could even baseline by taking a photo of the bike w/o the rider as a tare. It is not too difficult and cheaper than a wind tunnel.
In some cases though a reduced FA does not yeild a significant change in drag; that's where your feild tests will help. A curved back may be faster than a position with a perfectly flat back. The right helment shape is critical, too. Trying to find the tipping point and ~1.5 - 2 watts per position change isn't going to be easy without dozens of trials (and equipment options).
-SD
https://www.kickstarter.com/...bike-for-the-new-era