10 A Field Test for Calculating Aerodynamic Drag Area?

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.

There has been conventional methods described by engineer Rinard on his website. They are well and good.

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...

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0 I'm Back!

Alright, its a weekend here after the first week of classes. Some of the courses I'm taking are exciting. As I read about governing equation derivations for my computational fluid dynamics class (CFD - a technique of solving fluid equations numerically on a computer), here is an article I read this evening about CFD applications in sport equipment study - especially in cycling equipment. High tech modern cycling is much about light equipment and aerodynamic design, and there is staunch competition in the market between different manufacturers. A common CFD application that is used to study flow fields around a bicycle design is FLUENT. Here is this article discussing a study on crosswind effects on a cyclist with a rear solid disk wheel as opposed to normal wheel with spokes. The article discusses solid disk advantages and disadvantages, clearly illuminated by FLUENT.

Great way to start the new year is to study some interesting courses and work hard from the start!