It may be that the rider/racer lessens his effort on a too-big sized bike, as compared to the same rider/racer's effort on a just-right sized bike. On the just-right bike, the rider/racer exerts to get the best out of him and the bike, which is the reason for the just-right bike. (And he has to really know how to handle his bike!) On any other bike outside of his just-right sized bike, he doesn't go all out, he doesn't put maximum demands on himself and the bike, he enjoys a ride of relaxation.
Madison, Wisconsin USA