[CSBM5]

One main thing nobody has mentioned is the contact area of a bar versus standard inside car surfaces. If you head hits lets say the b-pillar, it is hitting a rather flat surface which allows the load of the impact to be spread over a rather large area of the head/face (also the surface deforms along with the head sliding on the surface, etc).

For a roll bar/cage bar, let's look at it unpadded for a moment. Think of the skull impacting the bar. The actual contact area is *very* small, a small piece of the outside radius of the bar times some small length of skull. The local stresses on the skull with be very high as little of the skull can "wrap" around the cylindrical surface to spread out the load area without significant damage. Hence one of the main concerns is that locally very high potential stress and the corresponding damage it causes.

Add the padding, and of course you increase the radius of the bar to some extent (slightly increasing contact area), but that might be negated by local compression of the padding upon impact. The basic nature of the problem that doesn't exist in normal car interiors still exists (very hard surface with very small contact area).