A Geeky Look at Wind Resistance

By Sam Hill

My friends and I spend a lot of time talking about things like aerobars vs. drops.

If anyone else is interested in the topic, here is some data. The photo, originally from Rolf Garthus's Hostel Shoppe in Stevens Point, WI, is a picture of  the same rider in five standard positions: sitting up, hoods, drops, aerobars, and recumbent.  



By imposing a grid on the pictures we estimated the frontal area the rider displays in each position. For example, assuming the rider is 6 feet tall in the upright position, this rider exposes 831 sq inches of frontal area when sitting up, 802 sq inches in the hoods, 763 sq inches on the drops, 607 sq inches on the aerobars, and 575 sq inches on the recumbent.  In lieu of a full spreadsheet we just give a chart that summarizes the relative frontal areas:




Bar 100%

Hoods 96%

Drops 92%

Aero 73%

Recum. 69%





A rider in aerobars would experience 27% less wind resistance to go the same speed as a rider sitting. The difference would be most noticeable at higher speeds.

Aerodynamics is really complicated stuff. They use wind tunnels because the equations are very nasty and still not very accurate. The only way to get real drag and  power output numbers  is to measure effects in a wind tunnel. But frontal area is a simple way to explain why it matters so much.

For anyone interested the actual spreadsheet with all the calculations is available for download at http://bloomingtonbicycleclub.org/private/blog/blogarchives/Rolf.xls