I was of the opinion that the flaps out were best for cool weather riding...last April, we rode in the NC mountains...42 degrees in the morning and I had them open. opening them makes your fairing 1.5"s wider and deflect more cold air off your legs.
I rode across the country, in 100 degree weather, to NAFO in July. Of course I had them closed. Was riding with ROADGLIDE, who had his opened and confidently told me that in hot weather, you should have them open, because it allows more air to mix into the engine heat behind the flaps...resulting in lower temp air blowing on your feet. So I tried it both ways for 10 days through Utah, CO., Texas and Oklahoma...and he was right.
So
- in extreme hot or cold - flaps out
- 60 - 90 degree weather - flaps in