Ah, so then the air temperature should reduce fuel consumption by 30%×30%=10%, which does seem to roughly match my experience. Thanks for pointing that out!
Internal combustion engines are actually more efficient in cold weather than hot weather. But the other factors like drag outweigh the increased efficiency of the engine. And since gas engines are so inefficient to begin with you don't notice much of a difference. https://physics.stackexchange.com/questions/270072/heated-an...