I know for a fact when animation dips below 24fps
Depends on the person. I can notice large drops in framerate. However, back on my first Voodoo1, while setting the in-game settings for Ultim@te Race Pro, I noticed that going down 1 frame per second at a time, 13fps was the lowest framerate that still appeared smooth to me. There was just a huge noticable difference between 12 and 13fps for me.
I'm not saying I'd enjoy a racer at 13fps. However, it would be TOLERABLE at 13fps as long as it never went above or below that. Any deviance at that framerate was noticable and annoying.