Adam, quote in context:
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HICS [federal Head Injury Criteria] and chest G's are generally lower in a 5-point than in a lap/shoulder belt. There's more ride down to absorb the crash forces since both the 5-point and vehicle belt stretch and the CRS shell flexes. That and the vehicle belt is 2 inches wide versus most CRS harnesses at 1.5 inches in width. The 1.5 typically stretches more.
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The way I read this, it seems the engineer is saying that the 5 point is a good thing for this particular measure; it reduces HICS and chest G's. I don't think he's saying the smaller belts are really worse. It's just that using the 5-point to hold the kid, and then the seat belt to hold the seat/kid combo to the car, there will be more overall motion since there are more points of compliance in the system (i.e.- the vehicle belt stretches, the 5 pt stretches, the seat deforms). That AND the 1.5" belts would typically be more compliant than the 2" vehicle belt, period. More points of compliance = more energy dissipative motion = better HICS and chest Gs.
Just thought I'd interject my interpretation.
-SJ
p.s.- one last thought... If we were just talking about belt stretch of a 1.5" belt in a 5 point config vs. 2" belt in 3 point config, there may be some good arguing regarding the amount of stretch. Assuming we look at belts mounted rigidly (take out the car seat from the equation) and we assume that the belt thickness is the same in both cases, and that there is no difference in belt weave or design, etc...blah blah, then in THEORY, the 5 point should stretch less PER BELT (or attachment point). Should be 20% less stretch for the 5 point case. Of course, designs vary and you can't be sure unless you compare one real design to another. I'll bet thicknesses of belts vary and other variable design factors have huge impacts on the amount of stretch of a particular belt....
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DEP '01 EX no-navi
[This message has been edited by shinjohn (edited 10-24-2001).]