On: Riding in a peloton is the most energy efficient locomotion – research (2018)

[vidanay]

Peregrine Falcon in a dive?

[InitialLastName → vidanay]

If you're only going to count the "going with gravity" part, a ball falling out of the sky is very efficient too.

[idontwantthis → InitialLastName]

Mountain bikes are most efficient when you ride them off a cliff.

[ummonk → vidanay]

If you count the gravitational energy extraction, it's probably not too efficient. Very streamlined shape but the high speeds cause a lot of drag.