I've been following Craig Vetter kinda loosely for awhile. He had long ago done a fuel efficiency competition with motorcycles on regular roads, the winner of the competition after 3 yrs achieved 470 miles/gallon. They relied on efficient streamlining. The reason I'm interested is to make the most of the electrons on an EV. Craig has been focused on a slightly different goal, a "Freedom Machine" that gets over 100 miles/gallon and can carry significant cargo (e.g. groceries) relying on efficient two-wheelers as the base vehicle.
He had started with a Honda Helix, stripping it down, and putting on a fairing. He spent nearly a year on this and came up with a fairly decent shape. I just read a test he did with his Son, his Son riding an unmodified Honda Helix and he riding the streamlined version. His Son was barely able to maintain 65 miles/hr at full throttle while he easily could do so at partial throttle and for him full throttle was 75 miles/hr. Pretty good but but not meeting the goal.
It seems recently he started rethinking the base vehicle and is asking for input. Seems the Helix wasn't quite sturdy enough.