THX, seat back braces are used almost no where else in the world in motorsports. It was originally brought about by roundey-round racers that want to use their aluminum Kirkeys and Ultra-shields that they have been using for years instead of dropping some major cash on a FIA seat that they might not even like. Yes, they are useful (and even mandatory in some sanctioning bodies)...especially for Aluminum seats.
If 40G survivability is good enough for the Naval Aerospace Medical Institute in jet fighters, it's good enough for me (and the FIA). Sure, accidents aren't though of as 100% fatal until over 90G's, but 27G's is enough to rupture your bladder and how many cars and cages will stay intact at anything over 50G's to protect the driver? The G's don't normally kill people...foreign object intrusion does.
Back on topic
Can anyone host my pics? They're way too big to post here and if I reduce them down, you won't be able to see much.