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From that web page:

<font face="Verdana, Arial" size="2">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. </font>
But there's only one single 2 inch belt across the child's chest with a belt positioning booster, while there are *two* 1.5 inch belts across his chest on the 5 point harness seat.

THAT'S a big difference when it comes to the forces involved and how they relate to belt stretching. Sure, they'll stretch more--per square inch. But there is more belt area, and less overall belt stretch per given force, than with the single 2 inch belt.

Did you know that suspension bridges--such as the Golden Gate Bridge--are held up by small strands of wire?

There's a reason they are suspended with lots of small strands carefully placed instead of fewer, larger wires. It's the same principle whereby I'd rather have two 1.5 inch belts instead of a single 2 inch belt.
 

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Adam, quote in context:
<font face="Verdana, Arial" size="2">
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.
</font>
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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[This message has been edited by shinjohn (edited 10-24-2001).]
 

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<font face="Verdana, Arial" size="2">Originally posted by 3odys4me:
It's *not* so clear after all.
http://boards2.parentsplace.com/messages/get/ppcarseats213/40.html

</font>
As I've said before, I will have no problem using a BPB for my son, unless he isn't mature enough to stay sitting correctly OR unless there is a reasonable alternative which is readily available.

I still think a 5-point harness is safer, but I doubt it is a huge difference, at least for children mature enough to remain seated properly.


As for stretch, remember that some stretch under strain is good. This increases the amount of time over which the body absorbs crash forces. That is provided the stretch is not enough to allow contact with another object in the vehicle, of course. Loose harnesses are bad, but stretch can be good. It should also be noted that many seatbelt systems have force limiters built-in. Some are mechanical systems in the tensioner, others are simply loops of belt that are held together by stitching that breaks under crash forces. All have the same function to increase the time the passenger can ride-down the crash.

It will be interesting to see the data when it becomes available.
 

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Discussion Starter #6
marvyn: I actually thought that this might make you feel better that a bpb is not necessarily inferior to a 5 point. Didn't you opt for a Britax bpb model? I may have a line on a place to get the super elite (5 pt) sooner than spring. Do you want to know about it if it comes through?

shinjohn: Makes sense. Your comment about "overall movement" is essentially what I was eluding too (in a less eloquent, less technical fashion) in previous posts. The overall point being that it is not obvious which type of seat is superior -- apparently performance is variable as related to the situation.

caviller: I respect your informed opinion. Would you be willing to render it on this seat?:

http://www.bopeepnurseryproducts.com/komfortgtx.htm

I'm trying to decide between the 5 pt Britax and this one. I Don't feel like I have enough safety related info on the komfortrider though. Thanks for whatever info you can offer. My 6 yr old son is tall and his current seat won't last (height wise) for another 30+ lbs. even though it is rated to 80 lbs.

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Unfortunately, I have no first hand experience with that model, either at check-up events, conferences or training. You might post your inquiry on the parentsplace forum linked by nyvram, I'm sure you'll get good input there.
 

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3odys,

Yes, that does make me feel better about my purchase but at the same time makes the whole issue a bit more confusing. At the risk of splitting hairs, I suppose I should feel reasonably sure that I made a good decision based on what products are currently available.

That's not to say I won't change my mind if/when the Britax 5pt becomes available.
 
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