Just kicking the wind tunnel 1x vs 2x data around in my head a little bit more today. I wish they would have done the baseline vs 1x comparison AT 20MPH instead of just the baseline. But I think the fact that they didn’t show such data sort of leads to its own conclusion. Anyhow, it’s interesting that the bike did stall at higher yaw angles at 20MPH, but the +ive/-ive yaw angle asymmetry did persist a little bit!
Note how the pronounced drag difference a yaw really collapses when you’re at a more intermediate speed! It’s reasonable to conclude that the 1x/2x drag difference also collapses. It’s probably de minimus at positive yaw angles (you might argue it was de minimus even at 30MPH!).
Drag difference collapses at lower speeds because (as we all know) drag varies with the cube of velocity. Drive train frictional losses, however, are linear with speed. As Jason has conclusively demonstrated in the past, drive train efficiency is also linear with rider output.
So as you slow down frictional losses start to dominate drag disadvantage. Even though drag disadvantage likely still persists.
If I consider three cases of i.) flat 40k TT, ii.) flat ultra tt, iii.) flat gravel ride which probably average ~27mph, 18mph-20mph, and ~16mph…then use Bicycle Bike Gear Ratio Speed and Cadence Calculator to pick out what gearing would propel me along at that speed with 90rpm cadence it looks like frictional drive train losses (1W loss vs 2x) would be about:
i.) 4.5W
ii.) 2.5W
iii.) 2W
If the course was flat and if I was confident there would be no mechanical issue with the 2x drive train I would be inclined to select 2x in the latter two cases and 1x in the former. But if it’s hilly 40k TT course I would still go with the 2x.
On the other hand! IF I could have infinite choice of chainring & cassette along with a derailleur that would shift it I’d probably pick 1x in all three cases. If you can make the gears big enough the 1x frictional disadvantage turns into an advantage. There just don’t exist the gear/derailleur combination that will do it.