Saturday, March 8, 2008

John Cobb Clinic

Last weekend John Cobb and I spoke at a TrainingBible Coaching camp in the Dallas area directed by Tom Rodgers. I always learn something when John speaks. As usual, there were several pearls.

John is one of the most experienced and knowledgeable people in the world when it comes to riding a bike aerodynamically. He spends countless hours in wind tunnels every year testing equipment and rider positions and has been doing this since 1984. He is also the brains behind equipment design for Blackwell Research. John may be best known for his work in helping Greg LeMond and Lance Armstrong with their equipment designs and positions on the bike when at the heights of their careers.

At the Texas camp John talked about several aerodynamics issues. The one that especially grabbed my attention was helmets. He said he had spent $11,000 recently buying time in a wind tunnel trying to determine the best helmets for various shoulder and back positions when time trialing or racing triathlon. What he found was that there was no relationship between aerodynamic helmet design and body position. There were a few lessons learned, however. Any aero helmet was ‘faster’ than any road helmet when in the aero position. But here’s the one that blew me away: Aero helmets are more aero when the tail is sticking up in the air (face looking down) than when the tail of the helmet is against the back. I’ve always believed just the opposite as it seems logical. I even wrote a blog on this last year.

But there was a caveat in John’s message. The reason why they are more aero when the helmet tail is pointing up has nothing to do with the tail of the helmet; it has to do with the air vents on the front. When the tail of the helmet is against the back and the rider is looking ahead the front air vents create a lot of turbulence which increases drag. When looking down so that the tail is raised the air flows around the helmet more smoothly since the vents aren’t exposed to the wind. So if you tape over the air vents the helmet creates much less drag and you go faster. But then you run the risk of overheating in a long race. I didn’t ask, but I logically assume (dare I do that again?) that with the vents taped the helmet is faster with the tail down than up. I’ll ask next time I see John.

To keep up with the latest in aero research visit John's blog.


At March 10, 2008 4:54 PM , Blogger Ron said...

By "fast", how much faster?

Looking down long term isn't very safe riding a bike. But for those naturally induced moments during high intensity, or for checking the numbers on a handlebar display, this 'may' be beneficial.

I also thought TT helmets don't have that many vents, in fact very little compared to the standard road issues.

Pro's can afford time in wind tunnels but the big picture is there's more percentage to frontal area in the rest of the body and bike than the head alone. Sacrificing safety, comfort, and noise reduction by looking at aerodynamics isn't really the way to go, especially with the head area.


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