Aerodynamics is one factor. Cold temps seem to affect gas mileage in a not good way. Thermostat closes when water temp drops to 169F if I remember correctly. It constantly opens and closes in cold weather and the water temp toggles up and down one or two degrees. My SC60 was similar to my NSC as far as gas mileage and all my CBRs got better gas mileage when cruising.
I had a CB500F that got around 38mpg on the highway.
I had a CB500F that got around 38mpg on the highway.