We all know and have seen professional cyclists with bent, flat backs over the aerobars or knees closer to the top tube while pedaling. The lore of aerodynamics is that drag increases as square of the velocity, so the faster you go, the double becomes the drag against you. The biggest area exposed to the wind is the cyclist himself, so the largest gains in speed are made if one minimizes or streamlines this exposed area. In mathematical terms, its called CdA.
Traditionally, aero drag area of a cyclist was measured in wind tunnels. But it has been found that the energy expenditures of operating the wind tunnels overwhelm the costs of the measurements. It is a big investment.
Ordinary folks (or extraordinary folks) sit on their saddles wondering how they can calculate/quantify this area. I have many times.
But if you want to sink your head deeper into numbers, there is a paper I discovered written by James C. Martin et. al. (from the University of Utah at Salt Lake) in 2006 describing in detail a field test that could be done by anyone with :
1. Microsoft EXCEL
2. A Power meter like PT or SRM
3. A nice stretch of road or a velodrome
4. Some knack for taking measurements and a pinch patience
Aerodynamic Drag Area of Cyclists Determined With Field Based Measures can now be accessed on the peer reviewed website, SportSci.Org in the Tests and Technology Section under Biomechanics category. The results can have slight errors compared to a wind tunnel (duh) but according to the paper, they are negligible.
Along with the free paper comes the EXCEL spreadsheet that you can play with!
What I like about this method is the fact that you can immediately get an idea of all the factors that play a role in dictating CdA. And you can get the experience being a bike scientist as well..
Head over there, bike freaks. This could get slightly addictive...