Why do most seats not allow RF tethering?

ajanes · Jul 11, 2009

I was asked if RF tethering is safer and or a preferable quality to have on a CR. Since only Britax and SK allow RF tethering is there a reason others haven't followed suit? I know the new TF w/ARB is essentially the same principle. What would your answer be?

Maedze · Jul 11, 2009

Some companies have chosen not to test that feature, or to build seats that can accomodate it, presumably to avoid added costs.

Other companies, like Recaro, believe that rear-facing tethering is detrimental.

andre149 · Jul 11, 2009

Out of curiosity... do we know their argument for it being detrimental? I'm guessing head excursion if the seat stops and the kid rebounds??

fyrfightermomma · Jul 12, 2009

An interesting note is why it's just SK and Britax. I believe the engineer for Sunshine Kids once worked at Britax, which explains why those are the only two companies allowing it in the US.

Weird that so many allow it in other countries, including companies that don't allow it here.

skylinphoto · Jul 12, 2009

I'm very interested in this discussion seeing as how I just ordered a RN last night and intend on tethering it rfing.

Keep it going everyone.

southpawboston · Jul 12, 2009

there was a NHTSA study done on the effects of swedish tethering (which we call RF tethering). i can email anyone the pdf if requested.

the conclusion was that there was consistent, albeit slight, reductions in injury measurements in RF tethered seats versus non-tethered. here is the text of the discussion and conclusions (with key points bolded by me):

DISCUSSION
Each restraint was positioned on the vehicle seat
with two primary objectives. The first was to
position the restraint with consistent angles because
installation angle is critical for young children, and
because restraint angle significantly affects injury
biomechanics. The second was to attach the child
restraint to the vehicle as tightly as possible. The
tension in the Swedish tether and the removal of the
foam spacer changed the restraint’s interaction with
the vehicle seat, and resulted in different lower
LATCH tensions. These varying tensions, however,
are the real world by-product of the addition of the
Swedish tether and represent a fundamental factor
that should be included when comparing the two
restraint conditions.
The addition of the tether had the practical
benefit of allowing better control of the child restraint
angle. Further studies are necessary, however, to
ensure that the addition of the Swedish tether does
not result in other misuse scenarios. Although the
tether tension is minimal during installation and
decreases to zero during the primary portion of the
frontal crash, strength requirements of the anchor
during rebound and in rear impacts must be analyzed.
The addition of a Swedish tether changed the
kinematics of the child restraints, although the results
varied between the child restraints tested. Rotations
and excursion distances of the upper portion of the
child restraint were reduced, which would reduce the
chance of the child restraints striking vehicle
structures such as front seats or the vehicle dash.
The effect of the Swedish tether on injury
measures was less consistent. The addition of the
tether generally caused an earlier onset of
accelerations, but there was not a concomitant
decrease in peak acceleration. The effects varied
across injury measures and across child restraint
model. Only six values (out of 30 calculated)
changed by more than 30%. In five of these six
instances, the tether resulted in reductions in injury
measures. All but one of these instances occurred in
the neck shear or moment measures, which are likely
the least biofidelic sensors in the CRABI dummy.
Thus, while the results varied, the overall effect of
the Swedish tether was a negligible reduction in
injury severity. Further testing on multiple vehicle
seats would provide more support for these findings.
Although not measured as part of this study, the
tether had significant effects on the lateral and
vertical coupling of the child restraint. Although
different coupling methods were tested, Kelly et al.
(1995) showed that increased coupling of the child
restraint to the vehicle improved test results in side
impacts. The increased rigidity afforded by Swedish
tethers would be expected to have benefits in side
crashes and rollovers, but this area requires more
research.
CONCLUSIONS
The results provide evidence that use of a
Swedish tether causes a positive but small benefit on
the injury risk to children in RFCRs in frontal crashes.
The advantage of tethers during installation and
possibly in other crash types (side impacts, rollovers)
suggests that the use of Swedish tethers in RFCR
could be beneficial. Further work is needed to
consider issues such as misuse, tether anchors, and
the effect in other crash modes.

Maedze · Jul 12, 2009

SPB, do you have any nerdly links on why Recaro is opposed (The First Years, too, I believe)?

ajanes · Jul 12, 2009

Maedze said:
SPB, do you have any nerdly links on why Recaro is opposed (The First Years, too, I believe)?

If First Years is opposed, why come out with the Premiere? I *think* the ARB works differently than the RF tether, but doesn't it achieve the same basic principle in stopping the car seat from cocooning? Maybe I'm all wrong and not really understanding the physics of it all. Please correct me if I'm wrong.

murphydog77 · Jul 12, 2009

ajanes said:
If First Years is opposed, why come out with the Premiere? I *think* the ARB works differently than the RF tether, but doesn't it achieve the same basic principle in stopping the car seat from cocooning? Maybe I'm all wrong and not really understanding the physics of it all. Please correct me if I'm wrong.

The ARB is different than a rf tether in the way it disperses energy, which is why Learning Curve is OK with it. Reps from Learning Curve (The First Years) have told me at the ABC Show and again at Lifesavers, I believe, that they think rf tethers cause too much accelerations on rebound because of the stiffness (the car seat stops when it reaches the end of the length of tether). There was some talk a while back that suggested that tethering a rf seat for a newborn and very young baby wasn't recommended because of that stiffness and potentially causing injuries. The ARB has some give to it.

ajanes · Jul 12, 2009

So at what age/weight would you recommend RF tethering? DS is now 8.5 months (I need to update my siggy, but I quite frankly I can't remember how I got it there to begin with) and weighs 19 lbs 5 oz. Would your RF tether a child of that age weight?

Maedze · Jul 12, 2009

Absolutely. I've never had to consider it for a child under 6 months as none of my kids fit in Britax convertibles before then, but I've always used the tether as soon as they've moved into them. (Wizard, Boulevard and Diplomat)

ketchupqueen · Jul 12, 2009

I used a Radian from birth for my third, and tethered from birth (well, okay, the very first day she was in it did not, because I wanted to just get her home. But the next time we went out I got in and did the tether.) I'd read the discussions and numbers on the risks and benefits, and to me, in my car, believed that the benefits weighed more heavily than the risks. So that's what I chose. Others, considering the same data, might choose differently.

Next baby I'm bringing home in a TFP, though.

southpawboston · Jul 19, 2009

Maedze said:
SPB, do you have any nerdly links on why Recaro is opposed (The First Years, too, I believe)?

i don't have links, but i did ask the main signo/como product engineer this question. something about the lack of standardization of RF tethers, and that you don't know how your RF tether point will behave in a crash. for example, what if you RF tethered to a part on the driver's seat, and the driver's seat loosened and moved forward several inches in a crash? that could cause an unacceptable increase in forward rotation of the CRS. at least for LATCH and seatbelts, those have been standardized and tested in each car. RF tethering is guesswork (hey, that thingamajiggy looks solid to me!! seriously, how can anyone of us judge how good an RF tether point is? ). i tend to agree with this. sure, it *may* improve the crash dynamics in most cases, but in a few extreme cases, may actually be catastrophic. and that study even concludes by saying that more research has to be done on potential misuse of RFT (such as by using a dangerous point or one that can move with the front seat-- someone else drives the car and moves the seat forward, not knowing the RFT is there--that would constitute misuse). i think recaro's stance is a very conservative one-- they probably know that the benefits of RFT are there (albiet small benefits, as the study i have shows), but that you are also introducing a complete unknown and untested variable, just like using plywood or eyebolts to secure a CRS in a car. while i don't necessarily favor nor disfavor RFT, i can totally understand why a company would take a stance against it.

god, i'm just glad my kiddos are FF now!!!

:duck:

Maedze · Jul 19, 2009

They could both be rear facing now

So Recaro's objection is merely to the lack of standardization and testing, not rearfacing tethering itself. That's actually reassuring.

southpawboston · Jul 19, 2009

Maedze said:
They could both be rear facing now

could be, but they're not, and i'm glad.

:duck:

So Recaro's objection is merely to the lack of standardization and testing, not rearfacing tethering itself. That's actually reassuring.

correct. and after thinking about it, i can totally see now how RF tethering can be risky. no one knows for sure how their RFT will perform in a crash. i would assume that britax has enough field data to support the use of the RFT despite only a mild benefit (that is, in frontal crashes; side crashes may hold more benefit for RFT), but it's still a big fat risk factor. what if the RFT point became dislodged and projectiled into your child's head? what if it caused the driver's seat to come loose? what if it interfered with the seat's airbag? how can any CPST or educated parent judge that? lack of standardization can be a big problem.

BananaBoat · Jul 19, 2009

ketchupqueen said:
Next baby I'm bringing home in a TFP, though.

Tell me why, tell me why......

ketchupqueen · Jul 20, 2009

SuzaBanana said:
Tell me why, tell me why......

Well, because then I don't have to weigh the benefits vs. the risks, it's the best of both worlds! Benefits without risks!

As mentioned above, while the ARB serves the same/similar function, the energy is dispersed differently.

Plus, it fits newborns well, and I

the Cranberry cover. And the install is nice too. And the tall shell.

Maedze · Jul 20, 2009

Ms. 57 flavors, how do you intend to get four babies in a Corolla

joolsplus3 · Jul 20, 2009

Combi Shuttle and Britax Chaperone have ARB's, for anyone who doesn't love the TF

And LOL SPB, I'd be glad for my kids to be FF in Signos, too

Why do most seats not allow RF tethering?

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