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.