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  1. #1
    edad03
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    Using latch and a seatbelt?

    I read on a previous thread that either a latch belt or a seat belt should be used to secure a car seat (the seat belt is best) but not both. Can some one tell me why?

    The reason I ask is that we have a Chrysler mini van with the Gen3 seat belts and after reading about the problems with theses belts, I am concerned about the safety of the Gen3 belts and think the redundancy of both the latch belt and seat belt would be an extra measure of safety.

    I apologize if this post is redudant. I did use the search function first.

    edad03

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  3. #2
    CPSDarren - Admin SafeDad's Avatar
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    Re: Using latch and a seatbelt?

    In general, you use whichever system results in a more secure installation for the child restraint. That is the one that is safer. It is not necessary to use both and using both may not be recommended by the owner's manuals. Like most aspects of carseat installations, there may be exceptions to this.

    The system automatically finds similar threads and includes them at the bottom of a topic, you can find more information if you click the links to those threads below.

  4. #3
    CPST/Firefighter Judi's Avatar
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    Re: Using latch and a seatbelt?

    What I was taught is if you use both, they may cause each other to fail, leaving nothing to hold the car seat in. If the child is foward facing, buckle the seat belt first, then put you car seat in, then use latch. There have been cases of lose seat belts being played with, by kids, bad results!

  5. #4
    CPS Technician Victorious4's Avatar
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    Re: Using latch and a seatbelt?

    It's important to follow both the carseat & vehicle manuals -- if they don't specifically say to use both LATCH + seatbelt together at the same time, then you must not.... Doing so may void liability & would also make your child a real life crash test dummy (since the seat is only tested to provide optimal safety protection with only 1 method, we do not know what would happen using both: both together may cause preventable injuries).
    TIFF ~ doula & all hours childcare provider
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  6. #5
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    Re: Using latch and a seatbelt?

    there's also the *chance* that using both methods together could *enhance* the security of the seat--we don't know, but the take-home message is that the testing has not been done AND there is the possibility of increased risk from using both, so for those reasons, it can't be done.
    Two girls, 7 and 6. Trek Mountain, Specialized Hotrock, Soma Buena Vista, Bike Friday tandem, and multiple other bikes. Oh, and a Mazda5.

  7. #6
    edad03
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    Re: Using latch and a seatbelt?

    Thank you very much for the replys.

  8. #7
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    Re: Using latch and a seatbelt?

    I had asked this same question to the customer service rep at Safeguard because I was curious. Her answer was as follows: "The reason you should not use both restraining devices together is because of the way that they distribute energy forces in the event of a crash. The whole purpose is to allow the child to, as gently as possible, "ride down" the crash forces. That's the easiest explanation that I can give you. "

    So it doesn't explain it in technical terms, but that was the answer I received.
    Jill




    Quote Originally Posted by edad03 View Post
    Thank you very much for the replys.

  9. #8
    Admin - CPS Technician joolsplus3's Avatar
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    Re: Using latch and a seatbelt?

    Quote Originally Posted by jmsherwood View Post
    I had asked this same question to the customer service rep at Safeguard because I was curious. Her answer was as follows: "The reason you should not use both restraining devices together is because of the way that they distribute energy forces in the event of a crash. The whole purpose is to allow the child to, as gently as possible, "ride down" the crash forces. That's the easiest explanation that I can give you. "

    So it doesn't explain it in technical terms, but that was the answer I received.
    Jill
    Julie
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  10. #9
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    Re: Using latch and a seatbelt?

    hmm... not sure i buy that.

    basically, that's saying that the movement caused by a stretching belt (LATCH OR seatbelt) is beneficial. yet, an ISOFIX (or fixed LATCH) connection eliminates virtually all movement of the restraint because you have a solid metal on metal connection, and that is one of its touted virtues.

    so again, not sure i buy that explanation.
    Two girls, 7 and 6. Trek Mountain, Specialized Hotrock, Soma Buena Vista, Bike Friday tandem, and multiple other bikes. Oh, and a Mazda5.

  11. #10
    Senior Community Member scatterbunny's Avatar
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    Re: Using latch and a seatbelt?

    Seatbelt webbing is designed to stretch to help absorb crash forces, to allow more ride-down time for the body. This is true, not something made-up by a carseat company to sell more seats.
    ~Jenny

    "When I was young, I admired clever people. Now that I am old, I admire kind people." ~Abraham Joshua Hesche

  12. #11
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    Re: Using latch and a seatbelt?

    Quote Originally Posted by scatterbunny View Post
    Seatbelt webbing is designed to stretch to help absorb crash forces, to allow more ride-down time for the body. This is true, not something made-up by a carseat company to sell more seats.
    i didn't say it wasn't true, i understand the physics and the benefit in a crash just fine, i just don't buy the argument that that's the reason not to use LATCH + seatbelts, because that doesn't explain what i mentioned above about ISOFIX. if that were the case, then ISOFIX would be bad.
    Two girls, 7 and 6. Trek Mountain, Specialized Hotrock, Soma Buena Vista, Bike Friday tandem, and multiple other bikes. Oh, and a Mazda5.

  13. #12
    Admin - CPS Technician joolsplus3's Avatar
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    Re: Using latch and a seatbelt?

    Quote Originally Posted by southpawboston View Post
    hmm... not sure i buy that.

    basically, that's saying that the movement caused by a stretching belt (LATCH OR seatbelt) is beneficial. yet, an ISOFIX (or fixed LATCH) connection eliminates virtually all movement of the restraint because you have a solid metal on metal connection, and that is one of its touted virtues.

    so again, not sure i buy that explanation.

    Rigid LATCH, for FF seats, is designed to pivot somewhat, Britax used to have this big whole explanation about how it actually moved during a crash to help lengthen ride down time, which reduces G forces on the chest. Remember the egg analogy? If the egg hits a wall and stops TOO fast, it cracks, but if there's some give like when your soft palm moves backwards as it catches, then it won't crack. Same with seats and kids, the rigid LATCH isn't as rigid as it appears, and the top tether is a strap, even a strap now with rip-stitch tethers, just like good seatbelts will rip out in a crash and absorb some of the forces (or have some other energy management device if not stitching that tears...)

    Julie
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  14. #13
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    Re: Using latch and a seatbelt?

    I could have also mentioned, she went on to say she was looking for more info in SafeRide News Publication to better explain it for me, but we never got that far. I had just wanted some kind of answer because I was more curious than anything else.
    Jill



    Quote Originally Posted by southpawboston View Post
    hmm... not sure i buy that.

    basically, that's saying that the movement caused by a stretching belt (LATCH OR seatbelt) is beneficial. yet, an ISOFIX (or fixed LATCH) connection eliminates virtually all movement of the restraint because you have a solid metal on metal connection, and that is one of its touted virtues.

    so again, not sure i buy that explanation.

  15. #14
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    Re: Using latch and a seatbelt?

    Quote Originally Posted by joolsplus3 View Post
    Rigid LATCH, for FF seats, is designed to pivot somewhat, Britax used to have this big whole explanation about how it actually moved during a crash to help lengthen ride down time, which reduces G forces on the chest. Remember the egg analogy? If the egg hits a wall and stops TOO fast, it cracks, but if there's some give like when your soft palm moves backwards as it catches, then it won't crack. Same with seats and kids, the rigid LATCH isn't as rigid as it appears, and the top tether is a strap, even a strap now with rip-stitch tethers, just like good seatbelts will rip out in a crash and absorb some of the forces (or have some other energy management device if not stitching that tears...)

    okay, that's closer to what i was looking for in terms of an explanation, but still... what you're saying then is that rigid LATCH is not completely rigid, there is some rotational allowance. but then, is it less rigid than having both LATCH belt and seatbelt together? i still don't think so.

    btw, i'm not trying to be argumentative about this, i'm really trying to get at the root of *why*, and from a physics standpoint, LATCH belt and seatbelt together are bad. i know they haven't been tested that way, and i know it's not allowed, and i would never do it of course, but i'm really looking for a technical explanation as to why... and so far i can't imagine the two together having *less* give than a rigid LATCH setup.
    Two girls, 7 and 6. Trek Mountain, Specialized Hotrock, Soma Buena Vista, Bike Friday tandem, and multiple other bikes. Oh, and a Mazda5.

  16. #15
    CPSDarren - Admin SafeDad's Avatar
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    Re: Using latch and a seatbelt?

    I think it's quite possible that on many seats in many vehicles, using both systems would not present any safety disadvantage. As mentioned, it may not be tested and therefore is not recommended and, of course, it may not offer any benefit, either. It is not impossible that the use of both systems could indeed cause the forces to be applied to the shell of the seat in a way that would be different than when tested one way or the other. You would hope that would not lead to a failure, but you never know unless it has been tested...

    This has been discussed among manufacturers and others in the industry, as many are looking for reasons to do this or not to do this. As is often the case with many issues of this type, we are stuck waiting until someone spends the money to do the testing before any manufacturer or agency recommends using both systems at the same time.

    Carseats are designed to be rigidly installed in the vehicle. The less movement, the better, though that is subject to diminishing returns. Keep in mind that the harness of the child seat will also stretch to some extent, just as the seatbelt can stretch. Rear seatbelt systems generally do not have the load limiting features found in front seats, except in some luxury and newer models. It's difficult to say where the tradeoff is between a rock solid installation in terms of reduced excursion and the benefits allowed by some energy management feature, such as a the load limiting features in such seatbelt systems. Some new carseats do have load limiting features included and this will also probably be a trend in the future.

    My understanding from some carseat manufacturers is that rigid LATCH systems are probably not significantly better than the higher end flexible LATCH systems (those with two separate straps and adjusters) in frontal crashes. On the other hand, there do appear to be benefits in side impacts, especially compared to seatbelt installations and flexible LATCH systems with a single strap/adjuster.

    Ultimately, if you have a good installation with a seatbelt, regular LATCH or rigid LATCH, your child is going to be safe if they are restrained correctly. Rigid LATCH may have some benefits, but I doubt the reduction in overall risk is significantly more than just having your child properly restrained in the back seat. Of course, rigid LATCH may make it quite a bit easier to get an excellent install, and that is important, too.

  17. #16
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    Re: Using latch and a seatbelt?

    thank you darren! that helps clear it up for me!
    Two girls, 7 and 6. Trek Mountain, Specialized Hotrock, Soma Buena Vista, Bike Friday tandem, and multiple other bikes. Oh, and a Mazda5.

  18. #17
    Carseat Crazy TheRealMacGyver's Avatar
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    Re: Using latch and a seatbelt?

    btw, i'm not trying to be argumentative about this, i'm really trying to get at the root of *why*, and from a physics standpoint, LATCH belt and seatbelt together are bad. i know they haven't been tested that way, and i know it's not allowed, and i would never do it of course, but i'm really looking for a technical explanation as to why... and so far i can't imagine the two together having *less* give than a rigid LATCH setup.
    I have to say I'm with Southpaw on this one, however, Darrens explanation makes perfectly good sense too. Being one that started here thinking more straps must be better, this topic really makes me wonder how many people(probably guys mostly) are using this same mentality in securing seats. It really makes reasonable sense that both MUST be better than one. I, like Southpaw, will not do this for the reasons mentioned, but a month ago...well you know what I would do Good thread, I would definately be interested in more research on this topic.
    Last edited by TheRealMacGyver; 03-29-2007 at 11:29 PM. Reason: commas added

  19. #18
    CPS Technician Victorious4's Avatar
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    Re: Using latch and a seatbelt?

    Because they're not tested that way we don't know how the crash forces would affect (or is it effect -- I'm tired) the frame.... It may cause stress on areas that it's not designed to withstand, which could cause injuries that are otherwise easily preventable: simply by following the directions We just go with what we *do* know & that is that one method or the other does provide optimal safety!
    TIFF ~ doula & all hours childcare provider
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