Using seats WAY past limits

[Wife&MomX3]

My friend has a very heavy younger 2 yo, about 42lbs. Their carseat only goes to 40lbs, so she is going to use all the money they get for Christmas to get him a HWH seat. Great, but until then she has turned him back RF. She saw a crash test video and she said it was haunting, so she cant bear him to not be RF. I guess she thinks that since he's over the weight limit for both RF and FF, that he may as well be RF, since it's normally safer. I told her I will lend her one of our HWH seats til Christmas, so he can be properly restrained. Wut can I tell or show her to make her realize that RF isnt safer if the child is 7lbs over the weight limit of the seat? R there any tests done, or stories of accidents showing seat failure when used so far over the limits? TIA!

 

[TechnoGranola]

Could you tell her that extra weight in the seat will cause the seat to have more downward rotation which means he will ramp up in the seat more likely causing his head to be above the shell of the car seat and leaving his exposed to be crushed by the vehicle seat in front of him when it comes back from its forward movement?

(this is early in the morning for my brain so if I have the crash dynamics wrong, someone please correct me!)

 

[LISmama810]

Rear-facing a kid that far over the limits is not safe. In a crash, rear-facing seats rotate down and toward the front of the car. The heavier a child is, the greater the risk of excessive downward rotation. That means that the seat could even flip over backwards, squishing the child between the seats. Also, a child that heavy is likely to be rather tall, so if his head is too close to the top of the seat, he could easily ramp up and strike his head on something during a crash. Generally there should be at least an inch of shell over his head.

I don't have any links right now, but hopefully someone will be by with some. Even a typical rear-facing crash test will show the rotation that occurs with children WITHIN the RF weight limits.

In the meantime, no, it's not ok to use a seat over either the RF or FF weight limits, but 2 lbs over the FF weight limit would be preferable, IMO, to 7-9 lbs over the RF weight limit. Ideally, though, she'll take you up on your offer and borrow one of your seats.

 

[Wife&MomX3]

He's actually not too tall, he's just freakishly heavy, lol. He's almost exactly a year younger than my dd1, and when he turned 1 and she turned 2, they were the same weight. Now @ 2y3m, he weighs as much as my (tall & skinny) going on 5yr old! He is just SOLID! Ppl try to pick him up and R shocked at how hard he is to lift, lol.
Thanx 4 the info on the downward rotation. I was trying to think of the physics of how the seat could/would fail.

 

[Pixels]

Rear-facing a kid that far over the limits is not safe. In a crash, rear-facing seats rotate down and toward the front of the car. The heavier a child is, the greater the risk of excessive downward rotation. That means that the seat could even flip over backwards, squishing the child between the seats. Also, a child that heavy is likely to be rather tall, so if his head is too close to the top of the seat, he could easily ramp up and strike his head on something during a crash. Generally there should be less than an inch of shell over his head.

Generally there should NOT be less than an inch of shell over his head. I know that was a typo, just wanted to make sure it was corrected.

Rear facing is safer because the shell supports the back and absorbs most of the crash force, rather than it going into the harness. But when the seat overrotates, the shell isn't there to take the force, because it has rotated away. The child is pushed up into the harness, putting all the force on the tops of the child's shoulders. This concentrates the force in two small areas, rather than having them spread out. Also, it can cause spinal compression.

If the child was in a forward facing seat, the harness would be able to spread the forces out across the hips, pelvis, chest and collar bones without concentrating it too much in one area. Also no spinal compression.

 

[LISmama810]

Generally there should NOT be less than an inch of shell over his head. I know that was a typo, just wanted to make sure it was corrected.

LOL, thanks for catching that. I'll go edit. Too early in the morning.