I was having a conversation at the LBS about TT position with a young (When you are 55+ everyone is young) man about the best aero postion. He has a degree from Georgia Tech in engineering and claims to be proficient in physics. I told him I thought it was important to keep your hands close, elbows in and head low. He stated that the hands & elbows only had to be inside the widest point of the body. He then asked me what bodypart I thought it would be. I offered shoulders. He stated that for most humans it is the hips when in a TT position.
My questions #1 is he correct, as long as hands & elbows are inside of largest body part, position within that frame is irrelevant? #2 Does the frontal shape matter Hands close & pointing so to speak, elbows in or would a brick do the same thing.
I don’t know much about physics myself but it doesn’t sound right to me either. I like to think in terms of fluids for aerodynamics and I wouldn’t want to dive into a pool with my hands apart. I would at least think that your hands being close together creating a wedge would be better.
There is a bunch of ways to skin the position aerodynamics cat.
The point I think the fellow at the LBS was getting at is that you can ride with as wide of arms as you want so long as you’re not increasing your frontal area. What I think is being ignored by him is the fact that some people’s shoulders get narrow when their arms are narrow and some people’s shoulders gets narrower when their arms are wide. The hole you create in the wind isn’t just determined by your widest part. Though, some people may see a decrease in coefficient of drag despite wide arms, I don’t think you would know without a wind tunnel.
What you seem to be thinking of is the Zabriskie/Lepheimer position. Basically closing off the stomach area from the wind by bringing your head down to your hands. I don’t think that Dave chose this position for no good reason. I also don’t know that the position works for everyone.
What I think the real answer should be, is that without a windtunnel it’s probably best to look to the majority of those using aerodynamics in fitting and the trends. Things like a rounded and low back, narrow shoulders, arms sheltering knees(or narrower), head lower than top of the back, etc. Without a wind tunnel or field testing, I don’t think anyone should stray from the guidelines that are easily identified from most top time trialists/triathletes. I would avoid things such as a drasticly wide arm pad position or the old Floyd Mantis position without data to know it works for me.