I think I missed a lot of opportunities to go faster when cruising and not taking advantage of tailwind. I find that if I put short effort in acceleration, the tailwind will take care most of the speed maintaining work.
For big tailwind I can usually see leaves rolling on along my general direction. Lately, I think if wind noise is more quite, I might be in tailwind?
So how can you tell if you've got tailwind or wind direction in general? (without flag anywhere nearby)