Seatbelts not locking for lightweight booster riders

christineka

New member
There's a discussion on this elsewhere, where smaller (under 50 pound) kids in boosters (some known to be properly used) are not held by the emergency lock mechanism on the seatbelt. I have some small, light kids. They fit in many harnessed car seats on the market and do ride in them in the main vehicle, but they ride in boosters in the car and on other occasions. This is concerning to me, though. I have the means to keep these kids in harnessed seats in all vehicles. (without even buying anything new) Do you think this is a valid concern? Has anyone else ever heard of this happening? Do you think by pre-locking the seatbelt, it might prevent the child from moving too much in the seatbelt in an accident?
 
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safeinthecar

Moderator - CPS Technician
A properly functioning elr retractor is not dependant on weight to function. They work on the principal of inertia.
 

Pixels

New member
A properly functioning elr retractor is not dependant on weight to function. They work on the principal of inertia.

This.

There's basically two ways that the seatbelt retractor "senses" a crash or sudden maneuver and "knows" to lock the belt. One is through the speed that the webbing is deploying. On vehicles with this system, you can yank on the belt fast and it will lock. Hondas are pretty sensitive and it's easy to lock the belt this way. The other system is through a pendulum. When the pendulum swings too far (which will happen in a crash or sudden maneuver), the belt locks. On these vehicles, you can yank on the belt hard and fast and it will never lock.

Neither system relies on the weight of the passenger.
 

christineka

New member
Why, then are there instances of kids flying out of their seatbelts, while the adult in the vehicle is held in place by the emergency locked seatbelt? Do kids make the seatbelt have different geometry? Or do the boosters get in the way?
 

luckyclov

New member
A properly functioning elr retractor is not dependant on weight to function. They work on the principal of inertia.
Yeah, that.

And I know this isn't an issue in Toyota, at least new(er) gen. An flea could lock my ELR at a complete stop from the jolt of a sneeze.:rolleyes:

Off-topic (well, sorta...), but there's a part in Horrible Bosses, where Jason Batemen's character is trying to flea the scene of a "crime" in his Prius, only his seatbelt locked and he couldn't get it on, and he said, "Oh, Toyota...". I had to explain to my friend why it made me snicker.
 
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Brianna

New member
Why, then are there instances of kids flying out of their seatbelts, while the adult in the vehicle is held in place by the emergency locked seatbelt? Do kids make the seatbelt have different geometry? Or do the boosters get in the way?

Which instances are you talking about? I recall a recent article about the girl being ejected, is there anything else?
 

jjordan

Moderator
This has definitely come up on this board before, and I believe Christine is referring to the current email discussion on the CPSP listserve. Those who are saying that weight is not a factor in a properly functioning ELR would, I suppose, assume that the ELR's in the cases being discussed were not working properly? If that is true then we have bigger problems, as ELR's are relied on to keep many passengers safe in crashes, not just those in boosters.

ETA: Here is one link to a previous post on this board where a seatbelt didn't lock when it should have, if weight were truly not an issue. Here is a thread with another case. (This second thread introduces the hypothesis that back seat seatbelts are perhaps not up to the standards of front seat seatbelts?)
 

luckyclov

New member
I either missed it or it wasn't stated, but was Bob's vehicle a Chrysler as well?

ETA: Nevermind. It was a Kia.
 

Pixels

New member
Here is a thread with another case. (This second thread introduces the hypothesis that back seat seatbelts are perhaps not up to the standards of front seat seatbelts?)

In response to the presentation linked in that thread:

Much of the conclusions that the back seat is not as safe as the front seat comes from testing with the HIII 10yo dummy and the high HIC values measured. This is the same dummy that has known problems with false HIC values - so bad, in fact, that HIC is not measured when testing child restraints with the 10yo dummy. During the crash sequence, sometimes the 10yo dummy has a chin-to-chest contact that results in a high HIC, but that doesn't happen in real life.

The problems with the 10yo dummy were known long before that study/presentation was written. The authors were, IMO, irresponsible to present such "evidence."

We can take away the real-world evidence that adults over the age of about 50 are safer in front always, 25-49 year olds are safer in front in vehicles with a frontal airbag, and everyone else is safer in back. That information comes from analysis of real-world crashes.
 

jjordan

Moderator
In response to the presentation linked in that thread:

Much of the conclusions that the back seat is not as safe as the front seat comes from testing with the HIII 10yo dummy and the high HIC values measured. This is the same dummy that has known problems with false HIC values - so bad, in fact, that HIC is not measured when testing child restraints with the 10yo dummy. During the crash sequence, sometimes the 10yo dummy has a chin-to-chest contact that results in a high HIC, but that doesn't happen in real life.

The problems with the 10yo dummy were known long before that study/presentation was written. The authors were, IMO, irresponsible to present such "evidence."

We can take away the real-world evidence that adults over the age of about 50 are safer in front always, 25-49 year olds are safer in front in vehicles with a frontal airbag, and everyone else is safer in back. That information comes from analysis of real-world crashes.

I didn't actually read the presentation linked in the thread I linked, I just noted a possible explanation for the seatbelt issue.

So, if there is no difference between front- and back-seat seatbelts, then what is the explanation for crashes where front seat seatbelts lock and back seat seatbelts do not lock on lighter riders? Either weight is a factor, or the seatbelts in the back are malfunctioning.

Several here (i.e. on this thread) have said that weight is categorically NOT a factor. If that is so, then we have seatbelt malfunctions.

Either way, we have a problem.
 

Pixels

New member
Or, the crash/maneuver is near the threshold for locking the belt or not. As I said in a previously linked thread, I know there are times that I resisted being thrown forward and therefore my belt did not lock. Other times, I didn't resist, and even though it was a lower vehicle acceleration my belt locked because my body was thrown forward harder.

I tend to let my body get thrown against the belt and let the belt lock and hold me back. DH doesn't, he tends to brace himself. My belt locks, his doesn't, all the time. Same vehicle, very similar body weights, different belt performance due to different reaction of the body in the belt.
 

luckyclov

New member
I tend to let my body get thrown against the belt and let the belt lock and hold me back. DH doesn't, he tends to brace himself. My belt locks, his doesn't, all the time. Same vehicle, very similar body weights, different belt performance due to different reaction of the body in the belt.
I tend to do the same. I wonder if any of this factors into non-tensed bodies receiving forces better/less severe injuries vs. a tensed body? Or did I just make that up? I could have sworn I've read that somewhere before.

At any rate, any time I have an "oh, crap!" moment in the car, I tend to keep my mouth shut so my passengers aren't alarmed and are less likely to tense or tense up as significantly. Whether or not that really plays any benefit, I guess I don't really know, but it's a habit at this point.
 

jjordan

Moderator
So, are you saying that weight has nothing to do with whether or not the belt meets the threshold for locking? Because I think it probably does have something to do with it. At the very least, someone who weighs less is possibly more able to resist being thrown forward.

But I also don't see how a child in a booster who has no idea that a crash is coming would "resist being thrown forward." Is it that the child's reflexes are quicker than the seatbelt locking mechanism? So, the child reacts to the crash more quickly than the seatbelt? If that is the case, I'm again seeing that weight may well be a factor.
 

Baylor

New member
I'm sorry if I'm sidelining. However do I need to test my belts ahead of time? I'm concerned about my son in booster now. He hovers at 50 lbs or so.

auto correct hates me
 

Keeanh

Well-known member
If seatbelts truly depended on a heavy weight to lock, then some seatbelt installs of car seats for light children wouldn't work either. Locking clip installs and lightweight locking latchplate installs both rely on the ELR functioning in a crash. And no car seat + baby combo is going to be over 50lbs until at least ~1yo.

No ELR mechanism relies on weight. If a properly functioning pendulum ELR doesn't lock, it means that there wasn't a sufficient change in the VEHICLE'S movement. That has nothing to do with who's riding in the belt. Even unoccupied belts "lock" with a pendulum mechanism. If it's dependent on the webbing's speed, that could be affected by a strong adult bracing themselves in an emergency braking situation. However no-one, not adults, and certainly not 50lb kids, are going to be able to brace themselves against a collision and reduce their speed enough to not lock the belts.

I'm not worried.
 

Keeanh

Well-known member
I'm sorry if I'm sidelining. However do I need to test my belts ahead of time? I'm concerned about my son in booster now. He hovers at 50 lbs or so.

auto correct hates me

If you want to test your belts, give them a good swift yank. If they lock, well, just yank them all and see if they lock. If they don't lock, that means you have pendulums. If you REALLY want to test those, let someone else drive (on an empty road) and have them hit the brakes hard so your body gets pushed against the belt. I'm sure you've "tested" your belts plenty of times. People just don't tend to notice that the belt is locked temporarily when the brakes are hit because their attention is on whatever made them brake, LOL.
 

safeinthecar

Moderator - CPS Technician
All retractors lock through inertia. S one are also feedback sensitive, but that is actually a designed to discourage leaning. If a child had introduced slack they could be ejected even through a locked belt. The weight of the passenger can indeed break the feed mechanism and cause a belt to remain locked post crash. This is much more likely with adults and can easily be confused as a failure to lock at all.

There is also the possibility that the retractor was broken( possibly due to prior crash) or had a foreign object in it prior to the crash.
 

Pixels

New member
All retractors lock through inertia. S one are also feedback sensitive, but that is actually a designed to discourage leaning. If a child had introduced slack they could be ejected even through a locked belt. The weight of the passenger can indeed break the feed mechanism and cause a belt to remain locked post crash. This is much more likely with adults and can easily be confused as a failure to lock at all.

There is also the possibility that the retractor was broken( possibly due to prior crash) or had a foreign object in it prior to the crash.

Or, it might not break, it might be designed to stay locked. My vehicle owner's manual tells me that in a crash that deploys the front airbags and seatbelt pretensioners, the belt will go into ALR mode and stay that way until the seatbelt is unbuckled. That way the belt stays tight through multiple impacts. Once the belt is unbuckled and allowed to go back into the retractor, it is supposed to return to normal ELR mode.
 

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