RF tethering - reasons, risks, benefits? (Split from "Has Anyone Bought a TruFit yet")

[fyrfightermomma]

This is just speculation, but would using the SK SafeStop or Britax RipStitch RF (which is a NO-NO and NOT approved) reduce the rebound head-excursion? My fear would be that using it would allow too much excursion if rear-ended to the point the child's head may hit the back of the seat. But doesn't the RF tether keep the car seat from going very far to the rear of the vehicle? It would be really interesting if SK or Britax would test with those features installed. Actually I don't know if Britax allows it RF, but I know SK doesn't.

Now I'm really confused and have no idea whether to RF tether or not, and we're getting ready to buy another seat.

Stephanie

I know what the SK safestop is but what is the Britax ripstitch???

 

[TechnoGranola]

there was a study by the university of virginia comparing a handful of convertible seats with and without RF tethering, looking at differences in head and chest loads during a frontal impact.

I just read this study and the following part stood out for me

In tests without the Swedish tether, a secondary tether was placed on the child restraint without any tension, and was only used to prevent the child restraint and dummy from striking the rigidized seat back during rebound.

So, even in the tests where NO tether was used, they USED a tether! And this was to stop the dummy from smashing into the seat back on rebound...isn't that part of what we wanted to find out in these crash tests? Whether a RF tether helped prevent injuries that would otherwise be sustained in a crash with a NON-tethered seat? In the real world, these seats would NOT have had tethers to prevent rebound, and I really would have liked to know what happened to the dummies in these cases.

They also tethered seats that were not designed to be RF tethered. I guess the good thing that comes out of this is that these seats didn't split or fall apart while tethered.

 

[skaterbabs]

Do you happen to have a link to the study? Someone had told me about it before, but I thought it was seatbelted passengers next to FF restraints? I thought the study didn't cover RF restraints? I haven't been able to locate it to read though, so I'm not sure. Would love to find out!

Although, my seatbelt child is NOT sitting next to the child restraint. The are both outboard. So, when the seat flies over into her seat, I still think it could cause injury. Perhaps if she was right next to the restraint, it might be different? I may be able to consider different positioning depending on which convertible I buy, so I need to read this study.

I don't have a link handy, but it was posted here on the forum a few months ago. There really isn't ANY evident that passenegrs are being struck by child restraints moving wildly, and a crash over 35 mph is considered unsurvivable by NHTSA.

While there are crashes at freeway speeds, they're pretty rare.

 

[southpawboston]

I just read this study and the following part stood out for me



So, even in the tests where NO tether was used, they USED a tether! And this was to stop the dummy from smashing into the seat back on rebound...isn't that part of what we wanted to find out in these crash tests? Whether a RF tether helped prevent injuries that would otherwise be sustained in a crash with a NON-tethered seat? In the real world, these seats would NOT have had tethers to prevent rebound, and I really would have liked to know what happened to the dummies in these cases.

They also tethered seats that were not designed to be RF tethered. I guess the good thing that comes out of this is that these seats didn't split or fall apart while tethered.

well, the way i read that was that the "loose" tether did not prevent the seat from cocooning, just prevented it from cocooning *all the way*, the same way that a door check allows your car door to open but keeps your car's door from opening beyond its intended path and denting the fender! the tether is like your car door's latch, not allowing the door to open at all.

the seat back in that study is a rigid panel, not a padded seat like you would find in a real car. i don't think the study was to see the effect of a child cocooning into the vehicle's seat back (i think the data out there already shows those forces are very low-- remember it's just rebound, and the head basically pushes into a "pillow" at low force). i think they were more interested in seeing whether the tether causes increased forward rotation (which it did) and also whether it causes an abrupt stop to the rebound following the forward rotation, causing forces on the head and chest as they want to continue rebounding while the seat is held by the tether.

at least that's how i read into it. :twocents:

 

[southpawboston]

I don't have a link handy, but it was posted here on the forum a few months ago. There really isn't ANY evident that passenegrs are being struck by child restraints moving wildly, and a crash over 35 mph is considered unsurvivable by NHTSA.

While there are crashes at freeway speeds, they're pretty rare.

isn't there a tech here whose daughter (or niece? i'm getting old, lol) was struck in the head by the outer edge of a carseat positioned next to her? this tech believes that she wouldn't have had that injury if there hadn't been a carseat next to her (there would have been just airspace). i am going to try to find that post.

EDIT: okay, i found it. it was defrost driving the vehicle and her friend's 7 yo was the one who got struck by the outer edge of the carseat next to her. this was in the thread that i started questioning the safety of being next to a carseat with a hard outer edge of a shell. so even if there isn't hard data on the safety of being seated next to a carseat, there is this anecdotal example of how it *can* be dangerous. i mean, think about it, the outside edge of a carseat shell is just as hard and edgy as a door panel. :twocents:

 

[TechnoGranola]

I don't have a link handy, but it was posted here on the forum a few months ago. There really isn't ANY evident that passenegrs are being struck by child restraints moving wildly, and a crash over 35 mph is considered unsurvivable by NHTSA.

While there are crashes at freeway speeds, they're pretty rare.

35 mph is only 56 km/hr, that is not freeway speed or highway speeds. The non-residential streets in our city have speed limits of 60 km/hr and people are usually speeding (GRRR!). Anyone turning left can easily be hit by someone going over 60 km/hr. Although, I assume that the vehicle going 60 will brake when they see they are about to crash into someone. And I guess I don't know how fast the braking will occur and what speed it will bring them down to by they time they impact. I will assume since the NHTSA is one of the experts on crashes, that the actual impact must be occurring at a much lower speed? and enough to make these crashes mostly survivable? I'd have to say that the most common crash I see is someone getting hit in the intersection when they are turning left.

 

[TechnoGranola]

EDIT: okay, i found it. it was defrost driving the vehicle and her friend's 7 yo was the one who got struck by the outer edge of the carseat next to her. this was in the thread that i started questioning the safety of being next to a carseat with a hard outer edge of a shell. so even if there isn't hard data on the safety of being seated next to a carseat, there is this anecdotal example of how it *can* be dangerous. i mean, think about it, the outside edge of a carseat shell is just as hard and edgy as a door panel. :twocents:

I only read the first post about the accident, so not sure if further details were provided later, but it wasn't clear if the little girl hit the car seat, or the car seat hit her. It did say she was in a lap belt only, I wonder if a shoulder belt would have made a difference *if* it was her body moving into the child restraint?

 

[southpawboston]

I only read the first post about the accident, so not sure if further details were provided later, but it wasn't clear if the little girl hit the car seat, or the car seat hit her. It did say she was in a lap belt only, I wonder if a shoulder belt would have made a difference *if* it was her body moving into the child restraint?

i'm supposing she hit the carseat, but what's the difference? the way i see it, if you are in a vehicle and too big to be in a carseat, you need to have an adequate head space to safely allow your head to move around and not hit anything hard. that's why we have side curtain airbags. the carseat becomes another hard object to hit when you are the seated passenger next to it. also, i don't think a 3-pt belt significantly reduces side to side movement of the upper torso and head.

 

[TechnoGranola]

i'm supposing she hit the carseat, but what's the difference? the way i see it, if you are in a vehicle and too big to be in a carseat, you need to have an adequate head space to safely allow your head to move around and not hit anything hard. that's why we have side curtain airbags. the carseat becomes another hard object to hit when you are the seated passenger next to it.

The difference would be that the shoulder belt would offer *some* protection from body movement. A lap belt only allows your upper body to move around more and thus perhaps contact something more violently.

ETA: I was cross posting this with your edit, so I think you have answered this already!

 

[southpawboston]

i think they should design carseats to have EPS foam and smooth sides on the outside of the shell to protect seated passengers next to the carseat! :thumbsup:

 

[TechnoGranola]

i think they should design carseats to have EPS foam and smooth sides on the outside of the shell to protect seated passengers next to the carseat! :thumbsup:

THAT is a great idea! I guess I need to look at the outsides of seats when we buy our convertible. That can be yet another one of my many criteria....

 

[skaterbabs]

I will assume since the NHTSA is one of the experts on crashes, that the actual impact must be occurring at a much lower speed? and enough to make these crashes mostly survivable?

The NHTSA test is 35 mph into a solid wall - it's the real-life equivelent of a 70 mph crash. Very, very few crashes happen at those speeds. Most (97%) are 35 mph or less, much more than that is considered unsurvivable. A crash in which a car impacts another object (car, tree, guardrail) at 40 mph is a pretty severe impact. For example, the crash force on an unrestrained ten-pound infant in a mere 10 mph crash is the same as if that infant had been dropped from a 5 story building.
Now imagine a 150 lb adult in a 45 mph crash - 6750 lbs of force are necessary to stop that person from moving. So the adult will impact the seatbelt with more than 3 tons of force. That's pretty much enough to snap the spinal column, crush the brain against the skull and fracture the sternum, even for a properly restrained passenger.

 

[crunchierthanthou]

i think they should design carseats to have EPS foam and smooth sides on the outside of the shell to protect seated passengers next to the carseat! :thumbsup:

I can just imagine in 10 years we'll be looking back saying "can you believe that we used those Britax convertibles with the awful lip on the shell? "

 

[southpawboston]

I can just imagine in 10 years we'll be looking back saying "can you believe that we used those Britax convertibles with the awful lip on the shell? "

i wouldn't be too surprised if that's the case! most convertibles today do seem to have a horrid lip which looks very uninviting to an oncoming skull. but it seems to be necessary for structural strength of the shell. the exceptions to this are the blow-molded shells, such as are found on the regent and recaro youngsport, which are essentially double-walled shells. the lip on a single-walled shell tries to accomplish the same thing as a double-walled shell, but more inexpensively.

 

[TechnoGranola]

The NHTSA test is 35 mph into a solid wall - it's the real-life equivelent of a 70 mph crash.

Can you tell me where you got this info? I took at look at NHTSA web site, and the test they use for cars is

Side-crash testing represents an intersection-type collision with a 3,015-pound barrier moving at 38.5 mph into a standing vehicle, with crash test dummies buckled in the driver and rear passenger seats. The moving barrier is covered with crushable material to replicate the front of a vehicle.

I know the NHTSA redid the CR reports for infant restraints because CR did them incorrectly (CR's tests were more like a 70 mph crash), but I was under the impression that the NHTSA replicated the tests PROPERLY so that they were actually at the desired speed?

 

[Jeanum]

A 30 or 35 mph real life impact ain't exactly gentle by any means. It's an incredibly forceful collision. :twocents:

 

[skaterbabs]

I was referring to the frontal crash test. Remember, CR's are not required to be tested in side impacts yet, the side impact test is for cars. So while NHTSA did redo the tests to more accurately reflect what would happen at the correct speed, a side impact crash at greater than 40-ish MPH is still considered unsurvivable. Again, 97% of all crashes are at less than 35 mph, and to engineer a seat that would withstand that additional 3%, it may not perform as well for lower-speed impacts.

 

[ginny4]

this is a very interesting thread & nto sure what to think

DH alone in his work truck so no children present. on a highway going 70mph blows a tire & teh truck flips several times but does land on all four tires eventually & thank goodness misses the trees. he WALKS OUT of the TRUCK uninjured. the EMS couldn't believe their eyes taht he was able to just WALK AWAY. he did go to hospital since it was work related to be check out. he was fine minus one small cut on his forhead from soemthing flying in truck that struck his head. if that isn't freakin amazing i don't know what is.
i'm sure bytime all this occured he wasn't going 70mph. the seatbelt SAVED his life regardless.
even tho there was no "true impact" otehr than the truck hittin the street a few times. i believe that even speedy accidents can be survivable. i wonder what a carseat would've done? scary thought however....

 

[TechnoGranola]

I was referring to the frontal crash test.

Okay, I didn't know you were talking about front impact. I see that it is meant to replicate 2 vehicles crashing into each other, each going 35 mph (so yes I can see that being like 70 mph if it's one vehicle crashing into a static object). I had been talking about side impact all along (my reasons for rear tethering and the crashes I see are side impact in intersections) which is why I got confused by your statement.

Remember, CR's are not required to be tested in side impacts yet, the side impact test is for cars. So while NHTSA did redo the tests to more accurately reflect what would happen at the correct speed, a side impact crash at greater than 40-ish MPH is still considered unsurvivable. Again, 97% of all crashes are at less than 35 mph, and to engineer a seat that would withstand that additional 3%, it may not perform as well for lower-speed impacts.

I realize that. It's not that I want the seats re-engineered to withstand higher crash speeds, but rather I am using the NHTSA side impact crash videos as a way to determine whether or not I want to rear tether.

 

[snowbird25ca]

In my CRST class we were told that we are NOT to RF tether at the clinics as RF tether has not been tested in canada - and to use it would possibly cause higher numbers for head excursion than are allowable in canada, vis-a-vis the US (which difference is, interestingly enough, why we always FF tether here). I talked to the woman who wrote the CRST manual and she does NOT recommend RF tether, especially when it will be anchored to some place that the vehicle manufacturer has not tested as an anchor point (ie swedish install). Basically, if it hasn't been tested, don't do it (and she seemed to imply that having the manufacturer say it was tested was not good enough).

This is incorrect. If a carseat manufacturer selling seats in Canada is telling parents it's ok to use their seat that way, then it has been tested in Canada that way. Canada's system of certifying carseats for sale is much different than in the US - in the US it's a self certification system. In Canada the manufacturer has to ship the seat to TC and TC performs the tests as per the manual and then gives the manufacturer a letter authorizing them to affix the CMVSS 213 sticker to the seat and sell the seat in Canada.

The East is taught very strongly not to rf tether, but my understanding from class is that this is NOT TC's official position. (My instructor has close contact with TC.) If it was, then we wouldn't be allowed to rf tether Britax seats. Manufacturers have to make changes to their seats for the CDN market sometimes - not allowing rf tethering in Canada is definitely one that could be made if it meant a seat didn't meet CDN standards. Simply put, if the seat didn't meet CDN standards when tethered rf'ing, then it wouldn't be allowed with CDN seats.

There's also the concept of trying to define head excursion with a rf'ing seat - because head excursion in a rf'ing seat wouldn't be measurable in the same way, nor does it pose the same risks as what it does in a ff'ing seat were it to be too high. Add to that, that there is no standard for head excursion in a rf'ing seat - probably because a) the risk of impacting the vehicle interior due to excess head excursion is already limited due to the seat being rf'ing, and b) the head excursion that would happen in a rf'ing seat is happening post-crash, not under the brunt of crash forces the same way as in a ff'ing seat.

* Note that the concern about head excursion with a ff'ing seat is the child's head impacting other occupants/or the vehicle interior causing greater injury, or having the child's head move further forward in the crash putting more strain on the neck. Neither of these have similar risks in a rf'ing carseat because rebound is not the same type of force as the initial impact that has caused rotation (in a rf'ing seat,) or head excursion (in a ff'ing seat,) in the first place.

This is just speculation, but would using the SK SafeStop or Britax RipStitch RF (which is a NO-NO and NOT approved) reduce the rebound head-excursion?

The Britax rip stitch tethers are on all of their convertible seats now, and they are not removable. I don't know how it might affect rebound head excursion though. :shrug-shoulders:

The safestop can't be used rf'ing, but the role the safestop plays is different than the rip stitch tether.. the safe stop allows the shoulder straps to move slightly - so in stead of the child's shoulders being held back tightly, the safestop has a small amount of give and the harness stretches out slightly allowing the shoulders a slight amount of movement with the neck and head - which is why it reduces neck loads - but it increases head excursion.