Why would Knuckle be slower? Youpi is really top heavy, so he might not be a fast runner. Pitou has been shown to enlarge her legs to gain the uber speed she has, but Youpi has been doing nothing but adding mass to his upper body, which should, by the same logic, make him not only slower but also clumsier when moving at high speed. Knucle has nothing to worry about as long as Youpi simply is following. But even Youpi might not be stupid enough to continue that for too long.