One thing that has had me wondering for a long time is the veracity of whether stays in a fully packed backpack really have any effect. Take my old Glen van Peski G4, which I still occasionally return to when I need a larger pack. It is, by UL standards these days, huge, and so can carry a lot of gear if you fill it up and that can be quite heavy. Every time I pack it full the entire body feels rigid and unbending and so I often wonder what it is about a frame that people aspire to. The gear itself within the pack basically holds up the load, making the pack a solid and rigid object that stays seem to add little to. You couldn't bend the pack even if you tried, and it is this rigidity which makes such packs as the Mariposa and Miniposa pull away from the shoulders when the stays are used. People talk about load transfer, but isn't the stiff, loaded pack already doing that?

I know that stays somehow make a difference, but I don't really understand how.

Well, like you stated, the lack of stays makes it pull away from you, so that would be one way to prove the effectiveness of the stays.

Well, actually, the Mariposa and Miniposa both have stays, and the stays are what make the packs pull away. Take out the included carbon fibre stays, or put in flexible ones (I use bamboo) and the packs pull in tight.

Hi Miguel,

If the stays are puling the pack away from your back, you need to have the stays bent to your back shape. The stays should be effective in transferring weight from the shoulder harness to the belt and visa-versa as needed.

David, the stays cant be bent because they are carbon fiber.

Miguel, Have you carried 35+ pounds in mariposa/miniposa? I believe this is where stays shine. I am not saying those carbon fiber stays are any good. The new mariposa comes with curved stays which I think are much better.

Hi David! I have the old Mariposa and Miniposa, not the newer ones with the aluminum stays. The old stays can't be bent.

But this still doesn't explain why the stays really do anything at all with a full pack. Try it. Pack a pack full with stays in, feel it, then take the stays out, and try to tell the difference. Do it with a traditional, heavier, internal frame backpack, too. If the hip belt and shoulder straps are snug and supportive, there should be little difference. (Of course I'm talking about a full pack, where the body of the pack itself is rigid).

Is it the difference in the way the front of a frameless pack versus a framed pack sags??? What is it about the cut of the Jam2 that makes such a difference?

Edited by butuki on 03/30/2009 09:16:31 MDT.

I had my Mariposa retrofitted with the new curved stays, so I wasn't thinking about it pulling away. Fits great with the new stays, and you can replace the carbon stays with aluminum arrow shafts bent to shape.

Hi Miguel,

Check out Frameless Backpacks: Engineering Analysis of the Load Carrying Performance of Selected Lightweight Packs and Quantitative Analysis of Backpack Suspension Performance by Dr. J. Aside from hopefully helping to answer your question, they are fine examples of BPL's roots.

The first article clearly shows that a McHale Subpop with stays clearly out performs one without in terms of torso collapse (the indicator used to measure load transfer) at total weights above 20 lbs, at least when the packs have a "soft good" density of 2.1 oz/L supplemented by weighted metal discs.

Ryan's analysis, however, focuses on claims that a rolled cylinder adds support, and pack density was not a tested variable. At first glance, the density (which would work out to about 6.6 lbs for a 50 L pack) doesn't sound like much, but you have to remember that some goods (like water, food, cooking gear, tent poles) aren't soft goods, so aren't included in that number. Unfortunately, the metal disks used may supplant the weight, but not volume of those other goods, so actual soft good density in a real world 50 L pack with 6.6lbs of soft goods may be somewhat higher.

The problem that I see with trying to increase soft good pack density to increase weight transfer (which may or may not work), is that at some point you may be damaging the lofting abilities of those goods.

If this question is really burning for you, I would by all means recommend taking his methodology, and adapting it to measure the effect of soft good density on torso collapse. I'd actually be quite interested in seeing that!

Edited by dsmontgomery on 03/30/2009 16:15:03 MDT.

Devin beat me too it - stays also prevent torso and frame collapse. I would also agree that they are not needed under 25 pounds or so given a frameless pack that is packed tight with either a rolled pad or a stiffer backpad. Over that type of weight, however, there is considerable torso collapse, at least in my experience.

Sorry guys - did not realize the earlier models did not have the aluminum stays.

Miguel,
Does that older pack have "load lifter" straps? I recently acquired a SMD Starlite; I have not had it on an overnight, but did try packing the same load three different ways. First with just a GG Nightlight sitpad in the pad sleeve, then with the sitpad and a 1/4 Thinlight rolled up for a "virtual" frame, and lastly, with the sitpad and stays. Both times without the stays I could feel a little torso collapse (a factor might be the lack of good compression options on the Starlite), and a very slight pull backwards. The load lifters helped alleviate the backwards pull well. With the stays in, the backwards pull was a lot more noticable, but the load lifters made it go away completely, and there was practically no weight on my shoulders. The same load felt much better.
Note that this is my first pack where going frameless is an option, so maybe the way I pack lends itself better to using the stays. The load lifters on this pack are also very well positioned (they attach at the same level as the top of the stays and right beside them) which I can't say for all the packs I've seen with them.

Devin, thanks for the links. Brings back memories of when I first joined BPL when it first started!

I just don't see how a pack manages to collapse when filled. In all my years carrying different packs, the only time a pack has ever "collapsed" was when it was under-packed. Otherwise all my packs have always been stiff and solid, one-piece sausages. And yet stays seem to make a difference with some packs.

What about while using a sleeping pad as a rolled-up cylindrical frame, and you incorporate the stays into the sleeping pad itself... will that not work? Must the stays be part of the structure of the pack itself? And must the stays always work with the hip belt? It is really curious. The reason I ask is I wonder how one might create a pack that can hold itself up without the added weight of stays. For instance, might inflatable airbeams, such as used in Nemo tents, incorporated into the pack body make it lighter and just as stiff? Would they even be necessary?

This is a timely thread for me, as I am thinking of purchasing an Ohm for my heavier loads with extra water. I find that my frameless packs tend to pull back where the shoulder pad connects to pack bag... only when carrying more than 12 pounds or more, with a pad that does not extend past the top of the straps. If I move a cylindrical pad up higher, it helps. Usually I am packing light enough where it is not an issue at all.

On my old Mountainsmith Frostfire, the stays are probably 4-6 inches taller than where the straps connect to the bag. And the load lifters are at the top near the stays. This does pull the bag forward and directs the load to the hips. I think my Gregory Whitney works the same way, but I have not looked at the construction closely to verify it.

For me, stays with load lifter allow me to get the weight off my shoulders. This would not be possible if the stays were not connected to the hipbelt. I have tried using load lifters without stays, with no joy. In fact, I have now gone to a LuxuryLite frame and hipbelt, as most of the UL packs I've tried, even with stays, can't really carry heavier loads with comfort (for me). If you are comfortable carrying a heavy and solid un-stayed pack , then consider yourself either lucky or very tough.

I'll throw in my two cents based on a couple of moderate day hikes with the GG Gorilla loaded with 23-25 lbs to simulate a long weekend+ of gear and food. With such a load, the pack is "full".

The aluminum stays plus the full pack are very effective in transferring virtually all the weight to the padded hipbelt. This pack does NOT have load lifters, but they don't seem to be needed in my experience thus far with the pack.

I am using only the sitpad as padding on the back (keeping the load closer) so that the curved stays work very well at transferring the load's weight to the hipbelt and keeping it close to the back. The shoulder straps carry relatively little of the weight and mostly serve to keep and stabilize the carry close to the body.

While body shapes, proportions and packing vary by individual, in this case the stays are (IMO) very effective in providing vertical stiffness without reliance on the burrito style of packing.

Edited by Beep on 03/30/2009 15:35:43 MDT.

Nick,

The Ohm has shoulder strap stabilizer/load lifter straps, that work very well for pulling the pack against your back and lifting the shoulder straps up slightly, aiding in load control and carrying comfort.

I have a Lowes 70+15 L pack with removeable stays. I can't bend it when it's truly full - even with the side compression strap loose. This is without using a burrito style rolled pad, or a flat-fold pad against the back. (ie: Thermarest folded in half lenghthwise, rolled and inserted on top of the sleeping bag, next to the clothing bag. However, the pack needs to be packed very tightly for this - about 1.5 times as dense as I usually pack. (ie: My "traditional" gear + most of my 2 kid's gear). The non-stretch nature of the very heavy duty fabric (500-100 Cordora ?) may also help.

Here's an interesting video from the manufacturer of a "compression pack" that claims stays aren't needed if you compress everything sufficiently.

http://www.youtube.com/watch?v=UXYi6flIGP4

Mike,

Thanks for the feedback.

I am waiting to hear back from ULA on some customizing questions, and will probably go for it. That way I can retire my Deuter Pro 40.

Hi Miguel,

You should read this:
http://www.bushwalking.org.au/FAQ/FAQ_PackTheory.htm

I ordered a SMD pack with stays and no matter what way i packed it, it pulled away from my back.

My vaportrail has no stays, but has a framesheet and padding and is great.

my 2 cents

Huzefa, thanks for the link! Yes, Roger Caffin's site. Another nostaligic site that I read religiously when I first started UL.

I'm wondering now if stays are more important in helping to keep a pack shaped to the curved human back than in transferring the load to the hips, since a packed pack tends to pull straight, even if the pack's sewing pattern, like that of the Jam2, contributes to a more ergonomic fit...