IIRC, wind resistance and aerodynamics start to become significant between 90-100 km/h. Up until then, the vehicle is spending more energy overcoming inertia and friction. After that, it's more about compressing and displacing the atmosphere in front of the vehicle. Pumping/compressing is energy intensive. That's why planes tend to cruise at high altitude, right? You can move more efficiently in a thinner atmosphere as long as you have enough air for lift and engine operation.As Private Pilot eluded to it can make a considerable fuel consumption to go much faster. I tried a few times and set my cruise at 100 km. I could easily get 4 days commute comfortably per tank. At 110, I can get approx 3.5 days of commute, but just barely. At 120 km, I can barely get 3 days in, the low fuel light comes on about 3/4 of the way home on the third day.