Originally Posted by DannoXYZ

Numbers can cause much more drag than leg-hair, although crumpling them doesn't help that much to reduce aero-drag. Even a badly-pinned crumpled number will cause significant aero-drag. You have to use the in-and-out pin technique to force the number to stay flush with the jersey. So each pin goes down into the number, down through the jersey, up through the jersey and up through the number. Two holes per pin through both the number AND jersey simultaneously. Ten holes total with 5 pins (at least one in the middle). This will keep the number from lifting away from the jersey and becoming a parachute, crumpled or not.