A teammate and I did some aero testing on Wednesday during our lunch ride. It was calm when we departed, so we planned to do coast-downs in various positions, comparing max speed.
Unfortunately, the wind did start up, and the first couple coast-downs were clearly invalid.
So, rather than waste the ride, we decided to head to a more flat course and try something new: One of us would ride in a repeatable static position (locked straight elbows, in the drops) and target 350W. The other, who was testing positions, would match speed from about six feet off to the side. Then we would compare power. Test runs would be 30 seconds, and we'd look at the average.
Well, on the bike, we were getting a fair bit of variability with identical positions, which was a little discouraging. We figured that the data on computers at home might tell us something useful, so we completed our tests, hoping for the best.
So, at home, we trimmed off the first and last 5" of each run and found that we were w/in 1% consistency on expected power. That wasn't enough to clarify his aero bar position decision (tipped up vs. flat), but it was enough to see the difference for me on the road bike between drops/locked elbows, drops/deep bend elbows, and IAB.
We're going to increase test duration and number of tests to see if we can separate the positions a bit more. We're trying to keep the speeds similar to competition speeds (25-27 for road positions, and 27-30 for TT positions).
Another analysis I'm going to do is to see if I can get an approximated CdA out of the numbers to see if we get more separation between the positions.
Anyway, I get a 10% power savings between locked straight elbows and a deep bend while in the drops. I usually relax in the drops with a 10-15 degree bend or so, which would probably put me at a 5-7% benefit for working down low.
IAB was about 2% more power required compared to deep bend in the drops, (which has my shoulders about 1.5" lower than IAB). The advantage here is that it's much more sustainable for long pulls. For short pulls though, and for establishing a break, it's good to know that I'm getting a good benefit by hunkering way down in front. I was thinking that would be the case, but there is a point that it would be too far down, and I don't know where that point might be.