|why a Camelbak? use bottles - more aero, according to John Cobb's latest tests at the A&M wind tunnel:
The cost of water bottles
7.7.03 by John Cobb
The pursuit of better technology is a humbling experience. For more than a decade Ive traveled to wind tunnels to perform tests on bikes and race cars and the athletes that ride and drive them, all in an attempt to demystify the conundrum of air in motion. The aerodynamic cost or benefit of water bottles has been a popular topic on internet forums in recent months, and my experience in testing themthe subject of this articlewas humbling because my results differed from my preconceptions, and from my public comments on the subject prior to doing the testing.
Back in '86 or '87 I tested water bottles in various locations on bikes and we learned some good things. Almost all the bikes at that time, however, had round tubing. Most of the bikes were made of steel. That tubing was not very large and the down and seat tubes were only just over an inch in diameter. There were a few aero tubes out of steel, but they were smalljust under a half inch wide by one and a quarter inches tall. This is half the size of todays aero aluminum and carbon shapes, in both the X and Y axis. These smaller tubes didn't test well with standard round bottles attached to them. We also didn't know anything about the relation of side winds to overall drag.
As the interest in the knowledge of aerodynamics picked up we were testing all kinds of things: equipment, body shapes, wheels, frames, helmets, and just an ongoing list of cycling-related products. As part of all this testing, a fewmost notably Jim Martindeveloped computer programs that helped us translate the effect of drag to ones bike time. I believe these time/drag calculaters are getting pretty good, and Ill apply some of them further in this article.
This most recent testing on several water bottle configurations took place at the Texas A&M wind tunnel. I chose a Quintana Roo Tiphoon in 55cm, which in terms of shape and style is a pretty representative bike. It had shaped aero tubes and was set up for triathlon racing, with Mavic Kysrium wheels front and rear, Syntace C2 clip-ons, pursuit bars, bar-end shifters and a round seat post with about 6cm showing. My test pilot was Bryan Cowan, who runs our Shreveport Bicycle Sports store. He's 5'10" and weighs about 150 lbs., races at the Ironman distance and occasionally joins me for a Krispy Kreme donut.
This was a pretty typical race setup, so as a reference point I started by testing the base line bike, with no bottles or cages anywhere, just rider and bike. I had decided that for this and all the water bottle tests I would use a "bell curve to try to estimate a real-world effort. I estimated, in other words, the percentage of time that I guessed each wind angle would be felt on the bike during a representative ride, so as to approximate the winds faced in a typical race. I used "0" yaw (meaning the rider would face no side winds), all the way up to 30 degrees of yaw, at 5-degree increments. I decided that 0 = 15%, meaning that no side winds would be experienced by the rider during 15% of his ride. Hed experience a