[jluetjen]

So far it doesn't look like you're doing anything dramatically different from anyone else. I'm not sure how you'd be able to actually "design" to those specifications without doing a bunch of FAE work first. There's an article on just this subject (Cage design for Rally Cars) in the most recent issue of "Racecar Engineering". Apparently the study was prompted by the spate of serious injuries and deaths which have affected the WRC in the last few years. I haven't read it through yet, but it appears that the problem of high-speed crashes from any direction (especially straight into the door) is a pretty complex problem.