C-Pillar Bar? Strut Bar?

[NoHachi]

It isn't..

For illustration: take a cardboard box. For ease of flex, remove the top (or if you're really a manly man, leave it on).

Now keep one end of the box fixed and push on one of the corners on the opposite side..you have just simulated typical suspension stresses on a chassis..

Now, take a tootpick or sate-thingy and mount that in the middle of the box..
Re-apply pressure and watch in awe as you see that bar mooves freely with the box and does absolutely zilch for structural rigidity...

Now mount the same tootpick in a diagonal fashion and observe why rollcages do work..