Relationship between perceptual speed and focal length

When I was a student at Gnomon learning virtual production with Dane Smith, Dane proposed an interesting theory in class: How do focal lengths change perceptual speed? It kept me up at night, the next day I rigged my car and did some fun tests.

Specifications

All tests are shot with the same cruise speed of 30mph, at 50mm, 135mm, and 300mm. As the video shows, at 50mm we experience the most perceptual speed when shooting towards the direction of travel (front view). From a lensing point of view, the longer focal length seems to squeeze space while providing a longer distance for reference substance, thus the same speed/distance of travel doesn't feel that much in the camera.

When it is perpendicular to the movement(side view), we feel the most speed at 300mm compared to 50mm. I'm assuming it is because a longer focal length restricts the field of view so that it gives less space for an object/or pixels to travel, resulting in a feeling of moving faster. (need tests need to be done on this)

As for rearview - perpendicular to the opposite direction of travel, 50mm appears to provide the fastest feeling of speed. I guess this is the same "space squeeze" effect.

Then, I shot some footage on 60fps, the results are almost identical. I also cropped the footage to mimic the FOV test, again, resulting in the same relationship between FOV and perceptual speed.

Test Videos

(Had no gimbal available at the time, sorry about the shakiness)

59.94fps side view