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From: "Gary Casey" <glcasey@adelphia.net>
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Subject: harness anchor points
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<<Today I receive additional images from Ron Laughlin and have added them
to the web page. It shows in more detail the harness over the seat back.>>

Now I'm not understanding the points being made.  From the looks of the
pictures the shoulder belts start at the seat back, go up and over the seat
back support crossmember (or whatever it's called), over the shoulders and
finally down to the buckle.  One has to assume that belts can only support
tension loads (no bending or compression) and therefore belt tension pulls
upward on the seatback which apparently is strong enough to support the
several thousand pound load that is possible.  Then the belt changes
direction over the crossmember to an angle that depends on the height of the
shoulders compared to the height of the crossmember.  The crossmember is
apparently strong enough to hold both the down-load and the forward load
from the occupant.  And finally, the belt changes angle again over the
shoulders to attach to the buckle.  The magnitude of that angle determines
the download on the shoulders during the impact, less angle giving less
download, but more belt tension for a given forward impact load, but the
download (compression load on the spine) cannot be eliminated.  With the
design shown the angle has nothing to do with the anchor point of the
harness and only the height of the crossmember.

The shoulder belt anchors in convertibles (cars) have always been a
challenge because the mounting has to be lower, increasing the spine
compression loading.  Most designs now loop over the seat back, which is
raised to be above the shoulder point for most drivers.  The higher the
anchor the less the compression loading.

My interest is in how to mount the anchors in my ES so they don't interfere
with the rear seat passengers.  The only existing "hard point" is the hoop
behind the door, but mounting an inertia reel there would affect the rear
seat passengers.  I'm tempted to put the reel further back, behind the rear
seatback and then put a high-strength bar, or hoop, behind the door for the
belt to angle downward.  The seatback itself won't hold a forward load so it
can't be used for this function.  How do others do it?

Gary Casey
ES #157