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

[minismom]

Re: Has anyone bought a True Fit yet?

It's also a 35mph crash though - probably not the most likely in real world experience.

Thanks Trudy I didn't know that was a 35mph test. I just knew they released it in reponse to the CR study, I guess it makes sense it would be 35mph. I'm not too concerned about cocooning either, just trying to decide whether that's better than a RF tether. I posted a similar thread in the tech forum. That video posted here about the head going out of the seat cause the tether holds the seat back got me a little nervous. I had assumed even though the RF tether wouldn't allow the seat to move with the child, that it would still reduce head excursion just like a FF tether. Am I wrong?

 

[snowbird25ca]

Re: Has anyone bought a True Fit yet?

Thanks, your 2 cents is much appreciated! I love how you form your posts (they make me consider other options and I never feel attacked), don't change a thing!

Thanks. That made my evening.

Thanks Trudy I didn't know that was a 35mph test. I just knew they released it in reponse to the CR study, I guess it makes sense it would be 35mph. I'm not too concerned about cocooning either, just trying to decide whether that's better than a RF tether. I posted a similar thread in the tech forum. That video posted here about the head going out of the seat cause the tether holds the seat back got me a little nervous. I had assumed even though the RF tether wouldn't allow the seat to move with the child, that it would still reduce head excursion just like a FF tether. Am I wrong?

Yes, NCAP standard is 35mph side impact, and the whole point of the CR test was that car seats should have to pass the same standards/speeds of tests as new vehicles do. The problem with CR test, is that due to the flawed methods, their tests equated to a 70mph side impact. So NHTSA redid the test using the 35mph side impact test that CR initially was trying to do, to see if they could reproduce the same failure rates.

Clear as mud, right?

Head excursion is a bit of a tricky thing, because in a ff'ing seat head excursion is measured from a point on the vehicle seat and the head can't cross the maximum distance from that point. During a crash, part of head excursion is also going to be the slight forward movement of the seat - if it's untethered there'll obviously be more movement, but even a tethered seat moves forward slightly as the webbing will stretch a little under crash forces.

The dynamics on a rf'ing seat are totally different though, so it's kind of like comparing apples to oranges in a way. Head excursion *should* be less with a rf'ing seat that is tethered, but that is going under the assumption that the rf'ing tether adds the same stability and reduces movement to the same degree as a ff'ing tether, and that isn't the case. Just to give you the image in your mind - ff'ing seat the tether starts tight, and the seat goes forward. Rf'ing, the initial stage of the crash the seat is going to rotate downwards towards the front of the vehicle - putting slack into the rf'ing tether. Then the seat will rebound, and at some point in the rebound the rf'ing tether will once again become taut and that's when the head excursion is going to happen.

My personal recommendations and belief about rf tethering is that in general it's a good thing and should be done whenever possible - with one exception - I would not rf tether the seat of a newborn child. We don't know for sure if there are increased neck loads on infants in a rf'ing tethered seat, but there is reason to believe that there could be. I wouldn't worry about a slight increase on an older child, but I'm not going to take any risk that might increase the neck load on a newborn. It would be a different story if we had seats like Australia where they have the rebound bar and then tether. (Australian tethering is where the tether goes from the back of the carseat shell, towards the back of the vehicle.) Australian tethering prevents or severely reduces the initial downward rotation, then the rebound bar reduces how much the seat can rebound. I would have no concern about increased loads on a newborns neck in that case.

And for the record, we're mostly speaking hypotheticals again, because we just don't have the real world crash data to say "under age "x" never use the rf'ing tether." or anything along similar lines. We don't have the real life experience to know if rf tethering changes the risk factors for injury - either positively or negatively. So in the meantime, parents are left to educate themselves and follow their carseat manuals. I wouldn't worry at all about rf tethering an older infant, but I'm just not comfy with the idea of putting a newborn in a rf'ing tethered seat. I'd use the seat untethered until the child got to be a little older. :twocents:

 

[TechnoGranola]

Re: Compass and rear tethering

The not rf'ing tethering came from a post that another member made quite awhile back after talking to some Compass engineers IIRC.

Compass is very strongly against rf tethering and they will not allow rf tethering. I don't know if they tested it that way or not... Maybe if you do a search for compass and tethering you'll come across the more detailed post?

If anyone comes across this post, please post a link. I searched and searched and could find people saying that Compass was against rear tethering, but couldn't find the post that talked about why or how someone found this out.

 

[jessclear]

It looks like there is strain put on the neck when the seat is tethered rf, and no strain on the neck when not tethered rf. Am I seeing this wrong? It seems when a seat is not tethered rf, the body stays in the seat and "cocoons" into the vehicle seat back. It seems as though the baby is more protected like this, rather than the tether stopping the seat and the child's head continuing to move toward the back of the seat. I have tethered my DD's DC, but I don't want to continue this practice if it will strain her neck in an accident. That is the whole reason I have her ERF, to protect her neck. Does anyone know Britax and Sunshine Kids' reason for adding the rf tether? Is there a reason to stop a seat from cocooning? I need to understand this better.
TIA

 

[AdventureMom]

Does anyone know Britax and Sunshine Kids' reason for adding the rf tether? Is there a reason to stop a seat from cocooning? I need to understand this better.
TIA

Here is a snippet from Britax's website:

Q. Can my Britax convertible car seat be tethered rear-facing?

A. Yes. Britax convertible car seats (e.g., Roundabout, Diplomat, Marathon, Decathlon, Boulevard) may be tethered when installed rear-facing. Britax recommends one of two modes of rear-facing tethering:

Australian Method:


This method requires the tether hook to be attached to a tether anchorage located to the rear of the vehicle.
Consult the vehicle's owner's manual for tether anchorage locations.
Use the same tether anchors as designated for forward-facing child seats.
This method controls forward rotation of the child seat in front impact crashes.


Swedish Method:

This method requires the tether hook be attached to a location to the front of the vehicle.
Consult the vehicle's owner's manual for tether anchor locations.
Do not attach to a tether anchor that is on the same seat as the child restraint system.
Attach to a strong structural point of the seat frame in front, the non-moving track to which the seat in front is attached, or the safety belt anchor of the seat in front.
A D-ring connector strap (anchor strap) is provided with each Britax convertible child seat to assist with this installation, if needed.
This method controls rebound of the child seat in front impact crashes and aids with achieving correct recline angle for newborns and infants.


Please consult for child seat's user guide for illustrations of these two methods.

FYI, the cocooning effect was not created on purpose but was an observation of what naturally occured during rebound. The majority of the crash force is the initial impact, so during rebound there is still alot less force on a child's neck than the initial impact. I agree with Trudy - I wouldn't RF a newborn or small infant. But I would an older infant/toddler/preschooler if the seat allows. I'm more concerned about the way the seat acts in a side-impact collision than a straight head-on collision. Even so, most collisions aren't a straight crash one way or the other - there's a diagonal hit, rollovers, secondary crashes, cars spinning around, etc. I think RF tethers can really add to the overall stability in those cases.

 

[tcottawa]

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).

 

[TechnoGranola]

It looks like there is strain put on the neck when the seat is tethered rf, and no strain on the neck when not tethered rf. Am I seeing this wrong? It seems when a seat is not tethered rf, the body stays in the seat and "cocoons" into the vehicle seat back. It seems as though the baby is more protected like this, rather than the tether stopping the seat and the child's head continuing to move toward the back of the seat. I have tethered my DD's DC, but I don't want to continue this practice if it will strain her neck in an accident. That is the whole reason I have her ERF, to protect her neck. Does anyone know Britax and Sunshine Kids' reason for adding the rf tether? Is there a reason to stop a seat from cocooning? I need to understand this better.
TIA

I found a discussion about this over the weekend (on this forum), I will try to dig it up. It seems that in countries where they practice extended rear-facing, seats usually have more than just a tether (and I think the tether location is different as well, not at the top of the seat?). They either have a stabilizing foot or a anti-rebound foot. In the case of a stabilizing foot, this would prevent some of the forward action that you see in that video, and the tether would not have near as much slack, and thus would not rebound with the same force or as much as it is in the video.

So, some people have the view that rear-tethering is great when combined with something that is going to act on the opposite force. The tether alone, maybe not so good. Although maybe the rear-tether alone is beneficial for side impacts, in that it prevents the side movement? Even if this is the case, I don't exactly want to trade one safety measure for another (i.e. good for side impact but not for frontal impact), I kind of want the best of all worlds!

ETA: I was cross posting with the 2 previous posts. AdventureMom has addressed the issue of rear tethering being beneficial in offset crashes and limiting the side movement of the seat. This is why I originally wanted to rear-tether, I just don't want to do it at the expense of creating more head excursion in a front collision!

 

[AdventureMom]

I also think the reason why other companies don't recommend RF tethers (other than it hasn't been crashtested) if b/c of what southpawboston reported on another thread after discussing the issue with Recaro: there is no standard RF tether anchor. So that would mean a company is taking liability for parents finding an anchor wherever they please. Even though they can say to attach it to a nonmoving part of the seatframe of the seat in front, that may not be possible in all cases. So parents are then left to find their own RF tether anchor - it could be not strong enough, too much of an angle off-center with the seat, etc. But the company may then be held liable for the outcome b/c they approved it to be tethered when RF knowing there is no standard place to anchor it. That's why it's hard to compare crashtests of RF tethered seats - in a crashtest you can anchor it just the right way, but it won't necessarily represent the way it is anchored in real life situations with no standard RF anchor, so the results of all the different variables lead to unknown behavior of the seat when tethered RF. Wow - did all that actually come out coherently?

 

[minismom]

I also think the reason why other companies don't recommend RF tethers (other than it hasn't been crashtested) if b/c of what southpawboston reported on another thread after discussing the issue with Recaro: there is no standard RF tether anchor. So that would mean a company is taking liability for parents finding an anchor wherever they please. Even though they can say to attach it to a nonmoving part of the seatframe of the seat in front, that may not be possible in all cases. So parents are then left to find their own RF tether anchor - it could be not strong enough, too much of an angle off-center with the seat, etc. But the company may then be held liable for the outcome b/c they approved it to be tethered when RF knowing there is no standard place to anchor it. That's why it's hard to compare crashtests of RF tethered seats - in a crashtest you can anchor it just the right way, but it won't necessarily represent the way it is anchored in real life situations with no standard RF anchor, so the results of all the different variables lead to unknown behavior of the seat when tethered RF. Wow - did all that actually come out coherently?

That makes a lot of sense. I really don't believe that all the companies that don't allow RF tether are doing it because they don't think it's safe. It can be a cost issue, or a liability issue. After all the FPSV doesnt allow RF tether and was made by Britax so obviously it had to do with not creating competition for Britax seats and keeping costs down not having to crash test one more feature. I agree that for most people finding a RF tether point is plenty complicated, and I'm sure most people who even have Britax or a Radian don't even tether it cause they just dont know how or assume it can't be done in their cars.

I agree with Trudy about not doing it for a newborn. I'm keeping dd's RA tethered as she's almost 13mo but it's not craked tight, whether that makes a difference or not I don't know. I really wouldn't want her seat flying all over the place in a side impact, roll over. Especially a seat that was outboard... About frontal imact, I think the rebound force is not as great, so you're still getting a huge benefit for being RF. Now, I see how her head goes forward when dh accelerates too hard and I do wonder what would happen if we got rear ended..

 

[RearFacingAdvocate]

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

 

[laccaycol]

I wonder if forcefully bracing the seat and tethering it would make a difference? That one seat isnt braced so it rotated downward more than it would have if it was braced. Right? Wouldnt that make a different outcome as well?

 

[southpawboston]

I wonder if forcefully bracing the seat and tethering it would make a difference? That one seat isnt braced so it rotated downward more than it would have if it was braced. Right? Wouldnt that make a different outcome as well?

i doubt that bracing does much in a severe frontal crash. remember that the front seat also readily bends forward in a crash, negating the bracing (as in, the front seat may move forward farther than the carseat rotates forward). then, upon rebound, the front seat may spring back and push back on the carseat, causing it to not rebound naturally, but with a catapulting push, KWIM?

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. the conclusions were that there may be a small overall improvement by RF tethering. however, the study did not examine the effect on side impact, which we suspect may be a greater advantage for RF tethering. interestingly, the data showed that in every case, RF tethering caused more forward rotation of the seat in an impact. despite this, the head criterion index (HIC) was lower in all cases with RF tethering.

 

[joolsplus3]

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 doubt the ripstitch tether would endure enough force to be ripped out, the rebound forces are very mild compared to the FF forces (which is why the tether connector strap and any solid bar are acceptable for RF tethering, the forces are minimal). The Safestop is for FF only.

Remember, the neckloads were increased on the other companies' tethered RF dummy, but were still well below the government maximum, there's no evidence at all to support the notion that a child will sustain any injury in a RF tethered seat. They RF tether in Sweden and have the lowest rates of injury in the world, by a huge margin, I think they know what they are doing with the RF tethering, honestly.

Edit: Ok, I said 'remember', yet again assuming someone had beat me to posting the carseat.org reference... here it is http://www.carseat.org/Technical/tech_update.htm#toptetherRF

 

[joolsplus3]

One alternative to RF tethering is the addition of a foot or in this case, handle, to prevent the seat from going back too far (the other video we have, of that Century convertible, doesn't show all the way to the end, where the dummy DOES violently slam into the vehicle seatback...it's edited to fool us into thinking that doesn't happen, I think). This may be preferable to high 'jerking' motion that a tether seems to make the neck have. Check out this evenflo seat in comparison to the Concord seat with the handle folded forward to act like an anti rebound bar http://www.childalert.co.uk/mov2.html. I doubt it would do much in a side impact crash.
Side impacts are really deadly...cars have not been designed to protect us in side impacts until very recently. And a rear tether does a great job in protecting against movement in those types of crashes (I did not attend the refresher/conference where this was shown, but I know some people who have).

Just something to think about....

 

[skaterbabs]

You may not know my views on why I want to rear tether yet (as I'm new here and have only posted about it briefly in very few threads), but my reasoning is NOT for protection of the child in the RF restraint (although if it helps them, that's cool with me!), but rather for my child, no longer in any form of restraint, sitting next to them. I watched the NHTSA side impact crash videos, and the seats do a wild flip into the seat beside them. This means my non-restraint child is getting whacked with some serious force from at least 50 pounds of toddler/seat (and as she grows, more weight obviously). I realized that my non-restraint child is also moving the same direction as the seat, but eventually she can't go anywhere once she hits the door, and that seat is still travelling towards her with great force.

Actually, there was a study done a while back that showed an increased amount of protection in a crash for seatbelt-only passengers seated next to a child restraint. The child restraint is NOT going to injure your older child in a crash based on the current research. Plus, more than 97% of all crashes are at UNDER 35 mph, that last 3% or so is basically considered an "unsurvivable" crash.
:twocents:

 

[Chex]

Check out this evenflo seat in comparison to the Concord seat with the handle folded forward to act like an anti rebound bar http://www.childalert.co.uk/mov2.html. I doubt it would do much in a side impact crash.

I watched that and I didn't like what I saw in either case. In the evenflo one, the baby's head slammed into the seat back and in the other one (braced by the handle), the baby's head seemed to catapult out of the seat. I just pray we're never in an accident. I don't like the thought of either of those scenarios happening. And as for which is safer, I don't know. In one, there could be some head injury, you would think. In the other, some spinal injury (possibly....it looked quite violent).

-Ann

 

[Chex]

Actually, there was a study done a while back that showed an increased amount of protection in a crash for seatbelt-only passengers seated next to a child restraint. The child restraint is NOT going to injure your older child in a crash based on the current research. Plus, more than 97% of all crashes are at UNDER 35 mph, that last 3% or so is basically considered an "unsurvivable" crash.
:twocents:

See, this is what I don't get. I know the studies are there, but there sure seem to be a lot of accidents on the freeway and there are usually injuries, but people walk away from them all the time. I know a lot happen during rush-hour, so people are going below the speed limit, but what about those that aren't during rush-hour? When people are going freeway speeds? I've seen a number of accidents on the news where people are slightly injured (there are plenty where they die, too), but it just seems that 35 mph is really a low speed for 97% of the crashes. (I'm not saying I don't believe it, it's just hard to swallow.)

-Ann

 

[TechnoGranola]

Actually, there was a study done a while back that showed an increased amount of protection in a crash for seatbelt-only passengers seated next to a child restraint. The child restraint is NOT going to injure your older child in a crash based on the current research. Plus, more than 97% of all crashes are at UNDER 35 mph, that last 3% or so is basically considered an "unsurvivable" crash.
:twocents:

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.

 

[TechnoGranola]

I watched that and I didn't like what I saw in either case. In the evenflo one, the baby's head slammed into the seat back and in the other one (braced by the handle), the baby's head seemed to catapult out of the seat. I just pray we're never in an accident. I don't like the thought of either of those scenarios happening. And as for which is safer, I don't know. In one, there could be some head injury, you would think. In the other, some spinal injury (possibly....it looked quite violent).

-Ann

I agree, those are BOTH mighty scary!

 

[TechnoGranola]

One alternative to RF tethering is the addition of a foot or in this case, handle, to prevent the seat from going back too far (the other video we have, of that Century convertible, doesn't show all the way to the end, where the dummy DOES violently slam into the vehicle seatback...it's edited to fool us into thinking that doesn't happen, I think).

Is the Century convertible video the one with the royal blue coloured convertible? If so, yes they make the crash look mild and don't show the rebound. Is there an extended version of that video? or any with a non-tethered RF convertible in a front or side crash?