I have talked of the 7th run and not said anything about it. This run was to test
both driver and passenger windows down halfway and their effect on the overall Cd. I run without A/C, so it is common for me to crack the window a little bit so I don't melt
However, what if I took it to an extreme for me? It
irks me to have
one window down halfway when I am up to speed. But am I just psyching myself out?
Let's see the data!
Run #7 Averages of the previous 6 runs
t=0 - 55 \ 55
t=1 - 48 \ 49.5
t=2 - 44 \ 44.5
t=3 - 39 \ 40
t=4 - 35 \ 36
t=5 - 31 \ 32.5
t=6 - 28 \ 29
All bias aside. Having both the windows down had an overall negative impact on coasting. However, the impact was extremely small! The speed of coasting with both windows up was equal to the coasting speed when both windows were down halfway, on occasion. The #7 run averages 1.25 mph at all data collection points during the test in comparison to the average of the previous 6 test.
What you can take away from this - as long as you are not a hardcore hypermiling stickler such as me, pushing limits and trying to squeeze every mist of fuel as efficiently as possible, then I doubt you will notice a difference in the real world having your windows down partially
Edit - There is no graph for the #7 test. I would need more runs to get an honest representation of the effect, and I only did one. Sorry y'all!