Question Balancing HE room in a packed vehicle

Carrie_R

Ambassador - CPS Technician
I rearranged my car to summer setup the other day and finally let myself be bothered by something that I've wondered about for a while. It's kind of technical, but I would really appreciate some input from those who enjoy the technical aspect discussions and/or have a good grasp on those portions of FMVSS, etc.

I have a lot of kids in my car. (I know this is news, lol ;)) They are all restrained according to best practice and I do my very best to not sacrifice one kid's safety for another. In respect to HE room, though, I don't know what the best way to balance this is.

Obviously HE for tethered seats < boosters, and HBB > backless because they sit the kid further forward. But then, almost all of my kids fall asleep (and crash HARD) at the end of a day of playing somewhere and really, really need their HBB. The front seat is also in use, so I can't slide it all the way forward.

For the sake of this discussion, assume that any parent is ok with what I come up with and leaves CPS decisions to me. In total, I need two RF seats, one HWH, two HBB and one backless.

I have two options for my third row, but either of them requires a RF seat on the 60 portion. Putting that seat there requires me to move the second row all the way forward.

Option A is booster/RF seat driver center in both rows, leaving ok HE room in the third row but not terribly much in the second row. I'm also having a problem with the second row RF seat touching the passenger seat (it's in the center,) which previously hadn't been a problem. A reinstall may fix that.

Option B is two RF seats in the third row, with two boosters or a booster and a HWH in the second row.

Seat on the 40 in the third row is either HBB (preferred) or backless, and then a HBB or HWH in the second; the depth of the 40s adjust independent of the 60 portions but I am also trying to get the front passenger seat back from the airbag as much as possible.

With current setup, third row booster riders (HBB) have 29" HE room, measured from the seatback behind them, second row NBB has 28" (with me closer up than I would prefer, 13" sternum to airbag,) and second row HWH has 25". He is in a tethered ProSport w/lap-shoulder install so I feel like he has pretty good HE control between the tether and the LBP, but I dunno? The front seat passenger has 35" between seatback and airbag.

I'm thinking about switching back to setup B. If I have the RFers in the third row, I could put a boostered child second row center (so no seat in front to hit, although there is a console,) tether the child behind the driver (leaving the RF Radian untethered,) scoot myself back a smidge and then balance the total HE room between the passenger side riders. If I leave a bit more for the third row rider and put the backless in the second row with a bit less, that might be ok. I also could *maybe* put the youngest booster rider (6) back in a HWH (Nautilus, which I should be getting back from loan soon) if he fits and tether it, and then "steal" some of his HE room for the 3rd row booster rider.

Is there a better plan that I'm not seeing? I left out ages/weights/kids/irrelevent seats to try to simplify a bit but I can supply if needed, if that makes a difference.

Another way of doing it, maybe make it a bit less confusing -- here's a map:

Driver // Passenger

13" sternum to wheel // 35" seatback to dash

NBB // RF // HWH
28" // N/A // 25"

HBB // RF // HBB
29" // N/A // 29"

After measuring, they're actually not as bad as I thought they were. I still don't love it, though, and would appreciate any ideas to balance the HE room as best as possible.

Really hoping a few of our technical experts can weigh in on this, since it is not one of my areas of expertise and I'm concerned there are facets that I am missing. I know it's a lot of info, so thanks in advance to anyone who managed to wade through it with their brains intact. :)

(I know I scare people away with my complicated novel threads; even if you don't have much input I'll take whatever you have. Even a bit of brainstorming is better than me alone.)

ETA: I posted all of this and then realized that it probably should have gone in the technical forum. Sigh. I apologize to whatever mod gets stuck moving it there. :(
 
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joolsplus3

Admin - CPS Technician
This is my brain on this post <fried egg>. :eek: :love:
I've never measured mine, I just try to scoot seats back and forth so everyone has maximum room in front of them :eek:
 

Pixels

New member
I believe the minimum recommendation for sternum to airbag is 10 inches. I think I have nine. I'd be over the moon with 13, but that's not going to happen unless I get pedal extenders, and then I'd have additional driver fatigue due to having to reach farther forward. My point is, as long as you are physically comfortable driving and have at least 10 inches clearance, I wouldn't worry about driver airbag space.

For the front passenger, that seat should be moved back far enough that the passenger is at least 10 inches back from the steering wheel. Look at the top right picture on this page: http://apps.volvocars.us/ownersdocs/1998/1998_SV90/98S90_004.htm. The passenger airbag and driver's airbag deploy approximately the same distance.

Backless < Highback is theoretical at best. I mean, it sort of makes sense, but they are held to the exact same standards. You're probably going to get a bigger variation by using Seat A instead of Seat B or just individual differences from one crash scenario to another. When they do the FMVSS compliance testing, I've seen where they test the exact same seat, with the exact same dummy, with the same installation, and the numbers are vastly different.

FMVSS standards are no more than 32 inches of head excursion for untethered seats; 28 inches for tethered seats. They start measuring from a point that is 4 inches behind the seat bight. If you have 28 inches for untethered seats and 24 inches for tethered seats, I think you're fine.
 

Carrie_R

Ambassador - CPS Technician
LOL Jools. That was my brain writing this post, too. :)

Pixels, thanks. I was fingers-crossed that you'd pop in here (and almost called you out by name :p) as I know you're great with all of the numbers and such. Front pass seat is parallel with or maybe slightly further back than me. I'm guessing I am normally 16-18" back... I'm not uncomfortable where I am, I just "feel" crowded because I'm normally further back. I'm not terribly tall (5'4") but I can have the Pilot's seat ALL the way back and still reach the pedals, although it's a bit stretchy.

I knew there was some funkiness with measuring from behind the seat, but I didn't realize it was so far back. (Aside, do you know WHY FMVSS is measured from 4" behind the seat bight? That seems so strange!) I thought I recalled the 32/28" numbers and that's what I was looking at, with the kids 3-4" short of those HE numbers. I feel a lot better knowing that they're pretty much within those limits. :)

Thanks to both of you for replying. I know posts about my vehicle (and others who have full vehicles) tend to be, uh, a lot... it's hard to find somebody to even peek at the challenge. :)
 

Pixels

New member
(Aside, do you know WHY FMVSS is measured from 4" behind the seat bight? That seems so strange!)

It's an arbitrary starting point. They start with that point, and then they "build" the bench on it. All measurements start from that point.
 

Carrie_R

Ambassador - CPS Technician
Ah, ok. That makes sense. The bench being built around the point, instead of vice versa. Thanks! :)

(And as an aside, I reinstalled the Radian and it's no longer bracing. If it won't stay, back in the third row it goes, lol.)
 

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