Rule #5 rides are hard rides, intended to render you a whimpering mess, laying about on the sofa complaining about your guns for the remainder of the afternoon. This ride classification is independent of terrain; this is a hard paced, attacking ride. Or, as Master Jaques put it:
The bike is a terrible thing that drives you to make excessive efforts, inhuman efforts.
Rule 5 Cogals are intended to test his theory.