That’s quite interesting. It makes sense, but I didn’t know they had done this.
One thing that I’d love to see one of these videos do is the treadmill experiment, but also have a fan that created a wind in the same direction as the treadmill, at the same speed. (Though I admit it would be very hard to set up well.)
This would highlight the fact that the effect depends on the differential between the ground speed and the wind speed, even when the kart is moving faster than the wind.