We used to occassionally race in an open Cub Scout event during a nearby Pack's regular PWD. One of those that is arranged so you buy lunch there and they make a few bucks off of that ... They had the infamous "hill" type stop section, though it was from a Wisconsin perspective "a mountain" ! Cars regularly fell off the far right lane onto the floor.
Sure enough, the year we were first really learning well about rail riding and prep, one of my boys had the fastest car we ever built. I still wasn't race smart though since we went there a week or two before our own Pack race. That boys' car not only fell off the hill a few times (onto the tile floor), it rolled on the floor and crashed into a table leg 8-10' away a couple of times. I pleaded with them to put something down on the floor to catch those cars, but they considered it an act of manhood or something. In fact, they finished their own PWD by running and smashing up all of their cars.
Needless to say, after some rework his car was never quite as fast as before that race. Big lesson learned.