southpawboston
New member
so i've been thinking a lot lately about the rebound phenomenon with RFing carseats. some say it's good, some say it's bad, some say it's just something that happens and it's neither good nor bad. it is what it is.
there are also pro-RF tethering and anti-RF tethering attitudes out there. britax obviously endorses the practice, as does sweden. on the other hand, recaro's stance is that it's just not standardized enough in its implementation to be reliable and there are too many vehicle-specific variances.
however, i was thinking that when is comes to anti-rebound designs, there's more than one way to skin a cat. the britax companion base has a rebound bar, which functions to minimize rebound, but by a completely different mechanism than an RF tether. it uses compression against the vehicle's seat back to counter rearward rotation.
this got me thinking, why don't all RF seats have some sort of bar, similar to the companion? that would take away the variability of an RF tether and the questionable choices of suitable anchor points. then it dawned on me... some RF seats are inherently better than others at preventing rebound, and they are this way for the same reason that the rebound bar on the companion works. they compress into the vehicle's seat back.
everyone here knows that a graco snugride and an RF scenera are very easy to rotate rearward, no matter how tightly they are installed. we've had both seats, and i've been able to rotate either seat at least 10-15 degrees without even trying, with minimal force. but, our evenflo triumph never rotated easily. and now, our new signo barely budges even an inch if i try to apply force on the top of the shell to try to rotate it rearwards.
it seems to me that the difference between the seats that can almost freely rotate and the ones that are more solid is whether they have a tall base, with a tall front edge of the seating area pushed into the vehicle seat back. the scenera is base-less. there is virtually no part of the seat that compresses into the vehicle seat back. same for the snugride base. but if you look at any pictures of an RFing britax, you will see that the base is relatively tall, and above the base, the front seat edge pushes very prominently into the vehicle seat back. the taller the seat (and therefore the farther away the compression into the seat back is from the hinge point, which is essentially the attachment point, or roughly, the seat bight), the more force it will require to rotate the carseat rearward. this is simple physics (work = force x distance). the work it takes to rotate the seat rearward is proportional to the force (compression against the seat back) times the distance (distance the seat compresses into the vehicle seat back; this distance is proportional to the height of the seat, relative to the seat bight).
and if you look at any comparison pics of a como/signo with a britax, you will see that the signo sits up even higher.
okay, i have to admit, i was kind of bored last night. the kids were asleep early, and we were waiting for the next netflix DVDs to arrive, so i fired up my CAD software and whipped up drawing to help illustrate this concept.
in (A), we have a typical infant seat base. notice how it doesn't compress greatly into the seat back. at least that is how our snugride base fit. look what happens when you rotate the seat (i've chosen 45 degrees of rotation for the illustration). there is very little resistance to rotation about the attachment point, because the base does not compress much into the seatback (focus on the area inside the gray circle). the small red line represents the belt path, and the green lines depict the pivot point (such as the lower anchors).
in (B), we have a base similar to the companion, with a rebound bar. notice how the rebound bar does its job by pushing against the seat back. think about how much force it would take for it to compress as far back as it is shown in the illustration. chances are, it would hit the metal frame of the seat long before it rotated that far.
in (C), we have a typical base-less seat like a scenera or uptown (or radian without the foot, which i believe is not allowed). again, there is little compression into the seat back, and if there is, it is not at a very far distance from the pivot point (seat bight). so the force required to compress into the seat back is less than if the compression were occurring farther away from the pivot point.
in (D), i've tried to illustrate how a tall convertible such as a britax or como/signo with a large base sits. notice how high the seat compresses into the vehicle seat back. it's almost like the rebound bar on the companion! and like the companion, if the seat were rotated 45 degrees, look how far the seat would have to intrude into the vehicle seat back. again, it would stop as it hit the vehicle seat frame.
so this is my deep thought for the day. of course these are only generic illustrations, but i would like to start comparing pics of different RF seats to see how high they sit and how deeply the squish into the vehicle seat back. i am also showing a pick of the signo installed in my car so illustrate how high the compression is relative to the seat bight.
my whole point here is that RF tethering serves a purpose, but there may be other design differences among seats designed to accomplish the same thing.
:twocents::twocents::twocents::twocents::twocents:
there are also pro-RF tethering and anti-RF tethering attitudes out there. britax obviously endorses the practice, as does sweden. on the other hand, recaro's stance is that it's just not standardized enough in its implementation to be reliable and there are too many vehicle-specific variances.
however, i was thinking that when is comes to anti-rebound designs, there's more than one way to skin a cat. the britax companion base has a rebound bar, which functions to minimize rebound, but by a completely different mechanism than an RF tether. it uses compression against the vehicle's seat back to counter rearward rotation.
this got me thinking, why don't all RF seats have some sort of bar, similar to the companion? that would take away the variability of an RF tether and the questionable choices of suitable anchor points. then it dawned on me... some RF seats are inherently better than others at preventing rebound, and they are this way for the same reason that the rebound bar on the companion works. they compress into the vehicle's seat back.
everyone here knows that a graco snugride and an RF scenera are very easy to rotate rearward, no matter how tightly they are installed. we've had both seats, and i've been able to rotate either seat at least 10-15 degrees without even trying, with minimal force. but, our evenflo triumph never rotated easily. and now, our new signo barely budges even an inch if i try to apply force on the top of the shell to try to rotate it rearwards.
it seems to me that the difference between the seats that can almost freely rotate and the ones that are more solid is whether they have a tall base, with a tall front edge of the seating area pushed into the vehicle seat back. the scenera is base-less. there is virtually no part of the seat that compresses into the vehicle seat back. same for the snugride base. but if you look at any pictures of an RFing britax, you will see that the base is relatively tall, and above the base, the front seat edge pushes very prominently into the vehicle seat back. the taller the seat (and therefore the farther away the compression into the seat back is from the hinge point, which is essentially the attachment point, or roughly, the seat bight), the more force it will require to rotate the carseat rearward. this is simple physics (work = force x distance). the work it takes to rotate the seat rearward is proportional to the force (compression against the seat back) times the distance (distance the seat compresses into the vehicle seat back; this distance is proportional to the height of the seat, relative to the seat bight).
and if you look at any comparison pics of a como/signo with a britax, you will see that the signo sits up even higher.
okay, i have to admit, i was kind of bored last night. the kids were asleep early, and we were waiting for the next netflix DVDs to arrive, so i fired up my CAD software and whipped up drawing to help illustrate this concept.
in (A), we have a typical infant seat base. notice how it doesn't compress greatly into the seat back. at least that is how our snugride base fit. look what happens when you rotate the seat (i've chosen 45 degrees of rotation for the illustration). there is very little resistance to rotation about the attachment point, because the base does not compress much into the seatback (focus on the area inside the gray circle). the small red line represents the belt path, and the green lines depict the pivot point (such as the lower anchors).
in (B), we have a base similar to the companion, with a rebound bar. notice how the rebound bar does its job by pushing against the seat back. think about how much force it would take for it to compress as far back as it is shown in the illustration. chances are, it would hit the metal frame of the seat long before it rotated that far.
in (C), we have a typical base-less seat like a scenera or uptown (or radian without the foot, which i believe is not allowed). again, there is little compression into the seat back, and if there is, it is not at a very far distance from the pivot point (seat bight). so the force required to compress into the seat back is less than if the compression were occurring farther away from the pivot point.
in (D), i've tried to illustrate how a tall convertible such as a britax or como/signo with a large base sits. notice how high the seat compresses into the vehicle seat back. it's almost like the rebound bar on the companion! and like the companion, if the seat were rotated 45 degrees, look how far the seat would have to intrude into the vehicle seat back. again, it would stop as it hit the vehicle seat frame.
so this is my deep thought for the day. of course these are only generic illustrations, but i would like to start comparing pics of different RF seats to see how high they sit and how deeply the squish into the vehicle seat back. i am also showing a pick of the signo installed in my car so illustrate how high the compression is relative to the seat bight.
my whole point here is that RF tethering serves a purpose, but there may be other design differences among seats designed to accomplish the same thing.
:twocents::twocents::twocents::twocents::twocents:
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