In all the years I have been riding, I am sickened to see how many
call mere "Engine Guards" crash bars. The closest to real crash bars
are what Dan has on his machine. Those have some of the design
to approach real crash bars.
The purpose of crash bars, by design, was to help keep a striking
vehicle bumper from snapping your leg off just below the knee, and
at slowing vehicle speeds (such as when the shocked driver hits his
brakes) strikes your crash bars and begins to roll you over. However,
with the design of the bars having a slope inward at the bottom the
bumper rolls you just until that slope, and then tends to 'spit' you
out and away from being run over.
The rear mounted curved bars also help to keep the machine off
you when you go down, and in some cases keep a bumper away
as well.
Now, there is not much any type of protection can help with a very
fast moving vehicle, or one that is continuing to accelerate when
you are struck.
Crash bars are not designed to wrap around, but for no more than
protection for you, and your machine. I wish I could find some made
to fit my 81 Interstate. I may one day just have to make some.