The center-of-gravity argument is an
excellent point. I'm going to introduce another argument, as well.
Ignore all the issues with headbanging, sliding, etc, for now -- let's assume a designer makes a PERFECT shoulder harness and a PERFECT lapbar.
Now get stuck upside down in a loop. Where would you rather have all your weight pressing against a restraint -- on some of the thinnest bones of your body (collarbones), or some of the thickest (thigh bones)?
To me, that right there should end the debate. Shoulder harnesses are an abomination. Even the mighty B&M, whose coasters I love, are wrong in this aspect.
Now, for some rides I CAN see them -- designing a lapbar restraint in an inverted ride would be an interesting trick. Ditto the standups -- shoulder harnesses there work as PART of a pretty elaborate system.
But for a good ol' sitdown, lapbars are the ONLY way to go...
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--Greg
http://www.pobox.com/~gregleg/