Hi. Watching the Giro on telly, it’s a TT with a steep long hill.
Although they are riding relatively slowly the riders are doing the hill in the aero position on the tri bars.
My understanding was that aero becomes less important the slower you are traveling. Is there a speed at which it’s negligible?
Not sure, but below 22 km/h is What I have heard
.
Going up the hills they were going as slow as 11km/h
Assume your CDA 0.2 in aero and .35 sitting up
Aero watts at that speed would be .5 * airdensity * cda * v^3 (assume no wind)
So at 11km/h
.5 * 1.18 * .2 * (11/3.6) = 3watts
.5 * 1.18 * .35 * (11/3.6) = 6watts
So if you can put out 10 watts more sitting up, you are still 7 watts ahead.
At 25km.h
.5 * 1.18 * .2 * (25/3.6) = 40watts
.5 * 1.18 * .35 * (25.3.6) = 69watts
So a 29 watts difference
So if you can produce 30watts sitting up, that is your break even point to sit up/
Theoretically 
That is truly amazing, thank you!