Hi Lismama,
being further away from point of impact means could easierly be changed to "further away from intrusion.
Yes, intrusion and passenger survival space are important, but only one factor. In addition, the farther you are from the point of impact, there is more structure to absorb energy and a potential for increased ride down time.
I believe that USA still has quite a large number of old cars on the roads. Europe has them too. Their chassis is softer than newer cars. What this means in real life crashes is that the old cars crumple more and the passenger compartment is more likely to be more intruded. Yet, with a soft and old chassis comes less crash loads on the child and the car seat
That is true in some cases. You can go back and find various vehicles in the USA that did well in IIHS offset tests and poorly in NHTSA frontal tests, usually indicating a chassis that was so stiff that it did well in intrusion but poorly for dummy kinematics. There are also vehicles at the opposite end of the spectrum like those you mention.
Most importantly, in the last couple decades, light trucks have accounted for about half of all passenger vehicle sales in the USA. Most of these are ladder-frame pickups and SUVs that have a relatively rigid structure. These vehicles are not only relatively stiff, but also relatively massive and prone to rollover. They also seem to remain in use a relatively long time. That is a substantial difference in the USA fleet compared to Western European nations I have visited.
In newer cars the crumble zone is greater because the chassis are stiffer in order to protect the adult occupants in the front seats better. passenger compartment intrusion is less likely to happen. Yet with a stiff chassis, the crash loads on the child and the car seats which often pose a real danger to the child have increased.
Right. The best new cars are a very fine balance of being stiff and designed well enough to resist intrusion, but also crumple well enough to reduce forces on the occupants. That is one benefit of having both a full frontal (NHTSA) crash test and an offset (IIHS) frontal crash test in the USA.
It is a fact that the less a child seat can move in a crash the more controlled the movement towards the point of impact will be, the less loads are passed on to the child. In other words you add ride down time to the crash as you let the car be the primary means of protecting the child.
Right, and the farther you are from the impact, the more energy absorbing chassis is between you and the impact. Also, because the back of the front seat can move more freely, relative to a rigid dash, it provides less coupling for a RF seat to the vehicle than you might expect.
A seat that is installed with a distance to the front seat or the dashboard (still legal in the US in cars with turn-off frontal airbags) moves uncontrolled to some extent and that adds crashloads on the child and the seat too - especially if the seat hits the structure in front of it. Ride down time is shortend. The front seat is a soft struvture that is more likely to move in a crash whereas a dashboard is stiff and holds the seat and the child better.
Right, and for that exact reason, since the front seat back is a soft stucture and moves in the same direction as the child restraint, it poses basically zero risk to an occupant in a rear-facing seat. Plus, as has been mentioned, rear-facing seats are quite forgiving of issues like this. Bracing or not bracing in the back seat is really likely to be a statistically insignificant improvement compared to simply having a rear-facing seat installed and used correctly in the back seat in the first place.
Another plus to frontseat installation (provided the airbag can be turned off) is better contact to a child that tends to become unsettled when seated in the backseat. front seat installation also adds legroom to the child in case you are using a European rearfacing seat such as the Multi-tech which is the car seat this thread is about. Thereby you are likely to get more rearfacing time for your child. For all these reasons.
A good point, though European seats that provide added legroom and a foot prop are not for sale in the USA or Canada and are rather pricey if imported. If you've researched the safety issues, understand the issues with importation, customs and local standards, purchased a model of this type and wish to brace it in the front seat when no active airbag is present and no restrictions are given in the manuals, then by all means do so. Your child will be extremely safe.
A rearfacing seat that is installed at an angel like 45 degrees with a little plus and minus, doesn´t have a supportleg and is not touching or braced on front seat or dash, has a greater downward rotation and the child in it rotates upwards towards the top of the seat. This would be a USA style rearfacing seat.
Right, at least a worst case installed one for a toddler or older child. Combined with a somewhat loose installation, it can rotate even more. Combined with a loose harness and ejection is a very real risk.
A rearfacing seat with a footprop that is also installed at less angle ie about 10 degree angle the downward rotation is vastly reduced and the rotation of the child mirrors that. The child moves INTO the seat and the seat moves away from the seatback. This would be a European style rearfacing seat such as the one in question here. The Britax Multi-Tech is a European rearfacing car seat with a supportleg and it is installed at an app 10 degree angle.
this guy explains this really well IMO. He has many many years of experience with car seats. He has a fantastic track record.
http://www.sikkerautostol.dk/2010/09/isofix-vs-bilseleseatbelt/
Hope this clears things up
Lena
Obviously, if we had the same vehicles, same child seats, same federal standards, same best practice polcies and other all the other factors present in Sweden, then this would be a moot conversation. But, the USA is quite different, as is true of Canada and many individual countries. That is exactly why it is generally a good idea to use seats approved for use in your own country and follow the given instructions. Of course, there are always exceptions based on specific circumstances.
Is this not a theoretical discussion at this point?
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Which brings me to my main point; blanket recommendations are never appropriate in the CPS world because our job is to educate, not recommend. We are good techs when we learn and share the whys.
Yes, it is presumably understood to be theoretical to the participants. But, in a public forum like this one, it's easy for a parent to find a single post on a search engine and come away with bad advice. That last point is one of my main points, also:
I certainly agree about blanket recommendations, especially if they are contrary to the instructions. Always follow the instructions if possible. If there is an exception based on a specific circumstance, then research and make an informed choice. In the case of bracing a RF seat, that choice will usually be fine, but not in all cases.
