Question Why do boosters have minimum weights?

wagonlover

New member
This is sort of a theoretical question. I'm wondering why boosters have minimum weights. I understand the reason for minimum ages and minimum heights, and that part of the reason for a minimum weight is to deter people from putting a child who is too young in a booster (e.g. a 2 year old who would meet a lower weight minimum.) Anyone know the reason for a minimum weight from a crash force perspective? I.e. are skinny children at more risk from using a seatbelt than higher weight children? Or is the weight minimum dictated by the size of crash test dummies?

The specific issue is that DD is very skinny, 4 yo, 39.5 in., 29 lbs. She is RF with no particular plans to booster her, or even to turn her forward at this point. But I need something for very occasional taxi travel, and a BubbleBum or Boostapak would otherwise be great. (I have an RSTV2 but she may be too skinny for that now.) I'm also trying to plan for future carseat configurations, but boosters may be out as she probably won't hit 40 lbs. for a few years.

Thank you in advance for input!
 
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ketchupqueen

CPST and ketchup snob
Staff member
There IS a weight below which the child will not load on the belt with sufficient force to lock it in a crash. It's somewhere between 30 and 40 lbs, but different tests say different things. It's quite possible that different boosters perform differently with a 33 vs. 40 lb. dummy (or child) in them because of the geometry of the seat and seatbelt as well. We do know that they are sure the booster will perform as it should with a child who meets the minimum weight (and other requirements.) For that reason, I would observe them. For your daughter, I'd look at a booster with a 30 lb. minimum rather than 40 if she hits 6 or 7 and is still not consistently 40 lbs. :)
 

1mommy

New member
I always wondered about the weight minimum with a lot of people saying they don't feel comfortable boostering a child below 40 pounds- even if that child is 6 or 7 years old. Wouldn't you run into the same issue with an infant seat then? I know this is all theoretical but if you had a 5 pound baby in a 15 pound infant seat that has lock offs, would the belt not lock in a crash because its below the weight minimum? I know its slightly different situation as it has the lock offs but those are pre-crash positioners as I understand it so they are only meant to hold the seat in place until the moment of the crash, right? Or what about if you had a baseless install and were using a locking clip to avoid the seat tilting?
 

wagonlover

New member
Thank you, that makes sense. I'll probably keep her harnessed for a while.

Any thoughts on taxi travel in this situation?
 

joolsplus3

Admin - CPS Technician
I always wondered about the weight minimum with a lot of people saying they don't feel comfortable boostering a child below 40 pounds- even if that child is 6 or 7 years old. Wouldn't you run into the same issue with an infant seat then? I know this is all theoretical but if you had a 5 pound baby in a 15 pound infant seat that has lock offs, would the belt not lock in a crash because its below the weight minimum? I know its slightly different situation as it has the lock offs but those are pre-crash positioners as I understand it so they are only meant to hold the seat in place until the moment of the crash, right? Or what about if you had a baseless install and were using a locking clip to avoid the seat tilting?

I think the problem with infant seats and labeling is that seats *require* shoulder straps to be at/below shoulders, and tiny babies don't fit properly according to the directions. 5 pound infants hardly cause seats to move (downward rotation, which is how infant seats are measured) in crash tests, so it's not really even an issue beyond rule-following.

Tiny people in boosters can be in danger if the car is using the "wrong" kind of seatbelt mechanism, this page on How Stuff Works is awesome to describe that http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/seatbelt3.htm

Plus Transport Canada has some evidence that smaller dummies, if not actual children (I'm not sure which) "Submarine" under the belt more (though the testing is also limited to some older models of seats, seat design has come a long way, fast).

OP, if the weight limit on your RSTV is 30, I'd be comfortable using it for travel. I used to use a large one on my barely-minimum kids and it positioned the belts properly despite them seeming too skinny for it. There are some backless boosters with a 30lb limit that you could use in a year or so more, when her shoulders have widened up a bit and it's easier to keep belts in position.
 

lourdes

Well-known member
I feel your pain! I have a 6.7 year old that weights 38 pounds... she is in booster since she was a little over 6 but I still regretted, just because she is so small.
 

1mommy

New member
I think the problem with infant seats and labeling is that seats *require* shoulder straps to be at/below shoulders, and tiny babies don't fit properly according to the directions. 5 pound infants hardly cause seats to move (downward rotation, which is how infant seats are measured) in crash tests, so it's not really even an issue beyond rule-following.

Tiny people in boosters can be in danger if the car is using the "wrong" kind of seatbelt mechanism, this page on How Stuff Works is awesome to describe that http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/seatbelt3.htm

Plus Transport Canada has some evidence that smaller dummies, if not actual children (I'm not sure which) "Submarine" under the belt more (though the testing is also limited to some older models of seats, seat design has come a long way, fast).

Thank you for that link, its fascinating to learn more about how seatbelts work!
 

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