Question Car seat weight testing - MT vs. FN, etc.

I don't understand the weight restrictions on car seats. Are the weights just reflective of what was tested, or indicate that a failure occured when the weight was exceeded?

The Britax Multi Tech can be harnessed longer rf by 15lbs than ff:

• Certified for rear facing use 9-25 kg. (20-55 lbs)
• Certified for forward facing use 9-18 kg. (20-40 lbs) with harness
• Certified for forward facing use 15-25 kg (33-55 lbs) with seat belt

All of the convertible car seats in the US that I can think of ff at higher weights than rf.

The Frontier doesn't rf at all, but it harnesses ff from 25lbs to 80lbs (40lbs more ff harnessed than the MT).

The Marathon only goes up to 35lbs rf, but can go 30lbs more ff (65lbs, which is 25lbs more ff than the MT).

Apparently Russ with SK said that the 35lb RA is the same design as the 33lb RA.

I don't understand. If the physical forces on the child in an actual crash are much less rf, then why do most car seats have a higher ff limit than rf?

Why does the MT go to lower ff weights than the FN and MA?

Is all of this just because car seat testing is really expensive, and the manufactures only test for what they consider to be marketable numbers? So is that why the MT doesn't go higher than 40lbs ff? Is it just becase they didn't test it higher?

Is there data out there that indicates what happens when a 45lb test dummy is rf in a seat that is labeled 35lbs rf and 65lbs ff? Or, is it just that this hasn't been tested, and therefore is not safe?

These are hard to answer questions because the MT´s "older brother" - The Britax Two Way Elite goes RF to 55 lbs and FF to 55lbs with the 5 point harness. The FF install is the same for both seats.

The TWE is just a smaller version of the Britax Regent, whereas the MT is a smaller version of the Frontier.

I would email Britax in Sweden about this.

Lena

First, the MT is tested according to different standards than the Frontier. It is not sold in the US so is not tested according to the US Standards.

We don't know what happens when a child (or dummy) above the stated limits is placed in a seat. We only know the information we have been given, that the seat is certified for X Y and Z. We can guess there is safety margin built in. How much? we don't know.

There's some skepticism about stuff Russ says. It seems he's a BIG fan of the Radian and will occasionally say stuff that is later contradicted. So don't take anything he says as gospel if they don't change it officially.

I am not sure how it all works but I was told that the us testing does not have standards for rf above 22 lbs and ff above 50 lbs. so I guess companies test to the 50 lb and 22 lb limits?? I was also told that the frontier would not pass higher weight limit testing without the top tether. My info came from Russ at skjp so maybe not completely true??
lotsolove

I think that info you (PP) got about not testing seats RF with dummies larger than the 22lb dummy was wrong. Mainly because other companies have admitted openly that they use the 35 pound 3 yo for RF . As for seats FF over 50, that's true, seats over 50 pounds are not legally required to meet the NHTSA compliance standards (head and knee excursion numbers and g-forces on the chest), but it's doubtful that those seats performing poorly with larger dummies, Sunshine Kids has proven how easy it is to meet the standards with a larger dummy.

Anyway, back to the OP... you can't compare different countries seats, who have different performance standards, slightly different dummies, different crash pulses, and most importantly different marketing and consumer bases, with US seats. They literally think higher weight harnessing is dangerous based on some measurement they do on the head (that no one can provide an English description for, so I'm fuzzy on it), so there's no market for HWH seats. And their harnessed seats might do just fine with a heavier dummy...but why spend money to rate it to that weight when they see no overwhelming market demand to recoup their expenses? (same reason we don't have huge ERF seats here, really... they don't think anyone will buy them, so no reason spending money to develop and test them... vicious economic cycle...). Also, boosters do have a good safety record. Why change what works well (speaking of Sweden...RF to 5ish, then in a booster..if it's as safe as it is, why sell seats that harness up to age 10 or so?)

Anyway, there're some theories for ya . Things are always changing... who knows what someone will decide about what's 'safest' next and it might take off worldwide, right?

Extended harnessing is not illigal in Europe. there are a couple of seats that harness to 80 lbs. One is the traveller Plus the other one is a Graco seat (new). They are sold as special needs seats. There is hardly a market for them in Europe, and the price tags are is about 1000 USD.and more. the only seat that is down to a reasonable price (Europe-wise) is the Britax Two Way Elite (app.:430 USD). 430 usd is normal but 1000 usd upwards is not.

There could be more to this, and that´s where Britax in Sweden come in.

Lena

Thanks, everyone, for your insight.

My question was more related to car seat testing and seat design in general, rather than the MT specifically. I was just using those seats as examples. It seams that the weights are more testing related, rather than failure related. Not that it really matters - the labels are the labels and must be followed. I was just curious behind the physics involved.

The force to the child is less, but I imagine it's worse for the seat. Look at the FF belt path on the MA vs the RF belt path. Nice, open, big... and then narrow and at the very front of the seat. And instead of holding the entire seat back, it's giving it this little pivot point.

As for why bother testing them higher, well... why bother? People in the US, by and large, will not RF past a year. Many won't do it that long. Yes, that may change... as people start Rfing to 2, 3 years, maybe seats will catch up. For the MT, well, that seat doesn't need to ever be used FF so might as well have it a RF only seat. FF harnessing is rare in that seat's home country. It's believe to be safer (and I tend to agree) to be in a booster at that age/weight. So if you can RF to 5-6 years old, why ever bother using it FF? Just move straight to booster and be done. I expect the FF weights are possibly there for kids who MUST, for one reason or another, face forward in a harness. And at that, according to them, it should be discontinued as soon as possible. Seems reasonable to me.