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  1. #1
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    Measuring bags by how many ping pong balls they hold

    I have been looking into getting a Tom Bihn bag, and as part of reading reviews, I came across this Wirecutter article which measures luggage by the number of ping-pong balls that they hold: https://thewirecutter.com/reviews/be...ry-on-luggage/

    Apart from it being just a cute way to measure, it seemed like a nice standardized way to compare capacities. I was wondering if perhaps Tom Bihn could consider doing this in the future for their bags?

    Measuring bags by how many ping pong balls they hold-carry-luggage-lowres-115-jpg

  2. #2
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    Well, that looks fun, but liters seems to work fine for me. Once I've filled a bag of known liters with my own stuff, I have a better feel for what more or less liters feels like.

  3. #3
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    That is not just a cute way....but the way it is done by the better and more honest manufacturers. No, not ping pong balls, but smaller ones, About 20mm. A bag is filled to capacity with these plastic balls and then they are measured in a cylinder that tells them the volume in liters. It's then converted to cubin inches.

    The reason ping pong balls are not used is that they leave too much space between them. And I believe it is how Tom Bihn measures their bags.
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  4. #4
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    It's ASTM F2153.

  5. #5
    Forum Member brucep's Avatar
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    Quote Originally Posted by G42 View Post
    It's ASTM F2153.
    https://www.astm.org/Standards/F2153.htm

  6. #6
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    Quote Originally Posted by brucep View Post
    Oh neat, very cool, thanks for pointing me to the ASTM test.

  7. #7
    TOM BIHN Crew (we work here) Darcy's Avatar
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    This has actually been quite the discussion topic 'round here the past few months.

    We have developed, and will implement in 2018, our own refined version of the ASTM standard.

    The 20mm (~0.75”) hard polypropylene balls on which the ASTM standard is based are great and we will continue to use them. The 20mm balls are superior to ping pong balls in two regards: as @Frank II mentioned ping pong balls leave quite a bit of space between the individual balls and are therefor less accurate for measuring small bags and pockets. Additionally, the heavier 20mm balls mimic more closely the density that one might expect from an actual load (clothes, shoes, books, etc) than do the less dense ping pong balls; that's important because the density of the load will cause the fabric and seams to ‘give’ (stretch, if you will) to a certain extent. Imagine filling your backpack with gravel: the weight (density) of the load would actually stretch your bag to make it bigger. The hard polypropylene balls don’t stretch a bag as much as gravel would, but the very light ping pong balls don’t stretch it at all.

    However, the element of the ASTM standard procedure that we’ve found problematic is this: per the standard, you fill the bag in question with the hard 20mm polypropylene balls, then you remove the balls and dump them into a graduated measuring cylinder. We’ve concluded that the measuring cylinder as specified by the ASTM standard produces a far sloppier result than if we weigh the balls contained by Bag X. The polypropylene balls are quite consistent in weight so it’s easy enough to determine how many balls (and therefor their effective volume) a specific weight of them equals. Furthermore, because our new method is more accurate than the ASTM, we can measure the volumes of much smaller bags and pouches (the ASTM standard specifies it cannot be used for volumes of less than four liters... though we already fudge that a bit.)

    As mentioned above, we will be implementing our own refined ASTM standard procedure over the course of 2018. Our resulting published volumes may or may not change from what we currently publish; they will still be one-for-one comparable with those of other manufacturers that use the ASTM F2153 standard, but will be more accurate than the strict ASTM standard procedure tends to produce.

    We'll announce the newly calculated volumes in a blog post that expands perhaps a bit further on this whole idea.... stay tuned.
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  8. #8
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    Quote Originally Posted by Darcy View Post
    As mentioned above, we will be implementing our own refined ASTM standard procedure over the course of 2018. Our resulting published volumes may or may not change from what we currently publish; they will still be one-for-one comparable with those of other manufacturers that use the ASTM F2153 standard, but will be more accurate than the strict ASTM standard procedure tends to produce.
    Just a thought, you should consider (once you finalize it) sending your revised protocol to the ASTM committee that F2153 falls under... they may consider it when they revise it next.

    Cheers

  9. #9
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    Thanks Darcy for the details of measuring bags! It's really cool to learn about the process behind-the-scenes.

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