Backpacking Weight Ranks
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Brett,
I agree that scloding a taller/larger person for carrying more weight than some tiny female gymnist is a bit silly. But we need SOME kind of metric.
We could get more complex about it, but who'd want to figure out:
PACK MASS INDEX (PMI)
(base weight in kg) / (hiker height in meters, squared)
or something like that?
Or, perhaps more clearly:
I modeled it after Body Mass Index, but I tried to keep it metric. Using (height in meters)^2 is an extremely rough surrogate for body surface area.
For those of you who can't think in metric:
PMI Trivia:
My current summer PMI is 1.26.
A 5'8.5" person carrying the 'standard' 10-pound pack would be almost PMI=1.5 So, what say we define UL as PMI<=1.5, for simplicity's sake?
Also, a 5'8.5" person with a 5-pound pack has PMI=0.75. Again, why don't we define SUL as PMI=0.75, which makes absolute sense as half of 1.5?
Oh, and to get a PMI=1 while carrying a 10-pound pack you'd have to be almost 7 feet tall.
But, to get a PMI=1 a 5'10" person needs a base pack weight just under 6.9 pounds. A noble goal.
Thus I propose that PMI=1 be assigned as some sort of milestone, too. Especially since 1 is a nice round number.
:o)
Can you tell I'm bored?
Okay, okay, this gets even better!
How about:
Pack Weight Index (PWI) using Avoirdupois units!
PWI = ((pack weight in pounds) / ((hiker height in inches)^2)) * 500
Or:
Under this system a 5'10.7" person with a 10-pound pack has a PWI = 1 and with a 5-pound pack his PWI = 0.5.
Now, THOSE are easy numbers to remember, and correlate perfectly with the already-established definitions of UL and SUL. It is ALWAYS good to define something important as equal to 1. We just have to remember that the 'standard Avoirdupois hiker' is defined as 5'10.7", a hair taller than the 'standard metric hiker.' Which seems appropriate, somehow.
Once you calculate and memorize your PWI for a 10-pound base pack weight it is easy to calculate it for any reasonable base pack weight- it is proportional. In keeping with my medical model I will refer to that as PWI10, and it is basically an obscure way to state your height. For instance, since I am 69.5 inches tall with a 10-pound base pack weight my PWI10 = 1.035. So, if I want to know what my PWI is carrying my standard summer 8.8-pound pack, I just multiply 1.035 x 8.8 / 10 = 0.91 !
Now you sasquatches out there can compare yourselves to the rest of us in a fair manner! Thusly: "Yeah, my pack may be over 10 pounds, but my PWI is still only 0.9 whereas your PWI is 1.2, Shortstuff!"
There! I am officially abandoning the PMI in favor of the PWI!
Of course even PWI isn't perfect. It assumes, for instance, that a taller person needs a heavier stove. Likewise for other gear that isn't dependent upon body size, like compass, tent-stakes, etc. But it probably WOULD allow a group to split up communal gear in a fair way- just try to have everybody's PWI equal.
REALLY bored. :o)
Someone should check my math…
Should we break this out into:
Base Pack Weight Index (BPWI)
Total Pack Weight Index (TPWI)
Skin-Out Weight Index (SOWI)
?SOWI might actually be the most rigorous of the three. Plus, you can pronounce it as one word. As the developer, I hereby set that as "sow we", rather than "sew we". However, SOMI will be "Sew me." Conform!
Ok, the new benchmark for the Lunatic Fringe among gram weenies is to attain a SOWI<1 !
>> True, but we were trying to equalize the thresholds for ease of attaining a pack that light – not ease of carrying it.
Well then we're talking about subtly different things. I sort of thought it would encompass a bit of both, ideally, since the whole point of going UL is to have a pack that is easier to carry. But, yes, after some thought I will agree that what you are saying is a more accurate characterization of the whining that we hear from the sasquatch people.
I will graciously concede. :o)
So, I guess we have to figure out a way to flatten the slope a bit? Any ideas on how to do that? Bearing in mind that we must have sound theory to back up whatever mechanism we come up with?
I guess that what we should do is survey 10-pound base weight packs of 5'10" individuals and see what percentage of the weight is considered "height dependent". Then we can further modify the formulae. For instance, if we decide that half of the average pack's weight is height dependent, then we can construct a formula that ignores half of the difference in height between the standard hiker and the actual hiker. (I actually think I can figure out how to do that…)
Who's up for performing the survey? :o)
Also, speaking of geek-off:
I was unhappy with the artificial origin of the 'standard Avoirdupois hiker' height, so I looked up some true average heights… Average human height worldwide is, coincidentally, 4'11" or so. But I didn't think that basing the PWI formula on that was really in the spirit of the thing since most of us are- admit it- western males.
So, ignoring extremes of age the average western male height seems to be about 5'10" or so. (The Swedish are a little taller, the French are a little shorter, etc.) With this as the height of the standard hiker the constant in the PWI formula should be 490, rather than 500, to make the average hiker's 10-pound pack result in a PWI = 1.
500 nonetheless results in a pretty good SWAG, and is easier to remember. But the "official" constant is now 490.
I could, of course, develop a similar constant for the PMI to correct for average height. As a matter of fact, if I'm going THAT far I could also make the constant such that a 5'10" hiker with a 10-pound pack produces a PMI = 1, so that it is identical to the PWI…
Do think it's worth the trouble? Or should I keep the metric formula "clean"?
EDIT—
Well, heck, it actually wasn't much trouble. The PMI constant would be 0.701, which I suppose we could round to 0.7 to make it easier to remember. We'll call that the "normalized" PMI, eh?
Actually, I guess that if I'm being intellectually honest then the PWI formula above is "normalized", too. I have adjusted the nomenclature in that first equation appropriately. Without the constant (be it 500 or 490) the Avoirdupois formula produces some very cumbersome numbers. (Even if you use feet instead of inches, UL is defines as about 0.3.) At least the non-normalized PMI formula (without the constant) produces wieldable numbers, as long as we are willing to concede the 5'8.5" 'standard metric hiker.'
I really like setting UL at unity, though! :o)
I will go further and clarify that unless otherwise specified, PWIn means BPWIn and PMIn means BPMin, and that by definition these ALWAYS factor in any item that is neither worn nor actually held in the hands while hiking, but including the weight of the actual pack, and less consumables. Thus, the gram weenies can't cheat on their BPMIn/BPWIn by having stuff in their pockets!
I invented it, so I can define it however I like. So there! :o)
So, now the normalized PMIn and normalized PWIn should be equivalent, with UL defined as unity. Or, you could multiply by another factor of ten, to produce a Height Adjusted Pack Weight Equivalent (HAPWE). In such a case, UL = PWIn x 10 = 10. Get it? It will produce a number equivalent in pounds to the weight of your pack for a 5'10" person. Then you can use whatever definitions you like for UL, SUL, or whatever. HAPWE may be cumbersome to calculate, but everyone will understand the value produced intuitively.
Yeah. I think I'll run with that…
Somebody please check my math. Better yet, somebody produce a proof that the two equations are equivalent… :o)
>>
1) Surely, any clothing, including socks and shoes, base layers, insulation layers, wind shells, rain shells, hats, gloves, etc.
2) Mosquito headnet? Kind of hard to find different sizes…
3) Sleeping system components, including bag/quilt, and pad.
4) Bivy? Shelter?
5) Stuff sack or compression sack for the bag/quilt?
6) Stuff sack for the clothes?
7) The pack itself?Using definitions THIS liberal, my summer pack weight is roughly 70% "height dependent."
Has anybody else calculated theirs yet? (I have realized that we needn't limit this to 5'10" people and 10-pound packs, because it will average out. It should be a normal curve.)
Should I change the list?
I recall that the sasquatches always complain that they can't fit into the lightest, smallest tents, so I wanted to keep shelter on the list. But should I? Likewise, for the bivy?
Do people with different torso lengths really end up buying different-sized packs often enough that I should include the pack? Or should I go with the "main stream" and just assume that most packs are the same size and just have adjustable frames, and exclude them?
Ok, here we go…
To adjust for the percentage of equipment that is "height dependent" in any of the equations above, replace the hiker height with their adjusted height.
Adjusted height is:
((( hikers true height – standard height )*R ) + standard height )
R is the "height-dependent ratio", so, for a 70% height-dependent weight, it is 0.7, get it?
Then just figure out the PMIn or PWIn as normal. And, if you want to generate a simple adjusted weight, multiply PWIn by 10 to produce the Avoirdupois HAPWE. (I've also crunched the numbers to produce a metric HAPWE.) Assuming that my 70% height-dependent weight ratio is accurate, here are some formulae:
Using these normalized PMI/PWI formulae, UL is defined as <=1. SUL is <=0.5. Etc.
The Avoirdupois HAPWE spits out a pack weight in pounds, and the metric HAPWE spits out a pack weight in kilograms.
Here is what a chart comparing Height-Adjusted Pack Weight Equivalents for people ranging in height from 4'11" to 6'5" carrying 10-pound packs:
HAPWE is, as Andrew wanted, a rough estimate of the difficulty of attaining a given pack weight if one is much smaller or larger than the "average" hiker, due to the simple fact that some of their equipment must be smaller or larger. This is NOT an adjustment for how burdensome it is for that person to carry a given pack. It is just a display of what the sasquatches have been complaining about.
For instance, according to the chart it is as hard for a 6'5" person to get his pack weight down to 10 pounds as it is for an average 5'10" person to get his pack weight down to 8.73 pounds. Fairly impressive. Likewise, a 4'11" person who gets her pack weight down to 10 pounds has overcome about the same difficulty as the average 5'10" person who got his pack weight down to 12.62 pounds. So, not quite so impressive. (Assuming, of course, that my estimate that R = 0.7 is accurate.)
And, if you crunch the numbers, a 6'5" sasquatch who gets his pack weight down to 11.45 pounds can claim to have managed his pack weight as well as a 5'10" guy who got his pack weight down into the UL range, 10 pounds.
Make sense?
As for defining how burdensome it is to carry a given pack, I maintain that PMIn or PWIn are better metrics than HAPWE. It is a harsh truth that bigger people can carry more weight more easily. I think that the steep slopes in Andrew's charts are probably pretty accurate that way. So, if we are trying to define UL as a given level of burden, then I propose a PMIn or PWIn of 1 as the definition. (After all, i developed the equations based upon a 5'10" individual with a 10-pound pack.) And thus a PMIn or PWIn of 0.5 defines SUL.
Again, somebody PLEASE check my math. It is getting late here, and I'm a little punchy.
Now we just need to agree on a value for R. Obviously, the lower this number the less that a hiker's height effects the HAPWE. I await your input…
Okay, I just figured out where those constants come from mathematically! Here is an ideal formula for Height-Adjusted Pack-Weight Equivalent:
W is the pack weight
H is the hiker's height (sasquatch or mouse…)
S is the 'standard hiker' height (which I propose be about 5'10")
R is the height-dependent ratio (which in my pack is 0.7, as I mentioned). This is a measure of what percentage of the weight of a standard 10-pound pack kitted out for the 'standard hiker' is 'height-dependent'.You can use any units that you like, as long as you are consistent. Specifically, if you input a height in inches then ALL heights must be in inches, etc.
The result will be a weight in whatever weight units you used, be it Avoirdupois or metric or whatever. You could enter weight in stone and height in hands, if one were so inclined, and it would spit out an equivalent pack weight in stone.
We'll call this the "Fellabaum-Dolman Equation". Having a hyphenated name lends it some gravitas, and I feel that I deserve top billing. Ryan, see to it that we are properly cited in the next edition of your book… :o)
Remember, HAPWE is the one that is sort of a measure of how hard it is to lighten your pack because you can't buy all size 'medium' gear like the 5'10" person can. Enter your height for H and your pack weight for W, and it will tell you what your pack weight would be if you were 5'10" and could buy standard sizes of the height-dependent gear.
(Obviously the real world doesn't quite work this way. There is a pretty broad range of body habitus that will fit into the same medium-sized shirt, for example, so there really isn't a weight penalty. HAPWE is most appropriate at the extremes of body size.)
So, say you are a 6'5" sasquatch, but you can't seem to get your pack weight below 11 pounds. Punch that into the formula and you will note that if you weren't stuck buying (heavier) super-sized gear your pack would only weigh 9.6 pounds! Feel good about that 11 pound pack, Sasquatch!
And of course you could produce a HASOWE by inputting your skin-out weight instead of your pack weight, too. But, obviously, R would have to be larger, because a greater proportion of the weight we are measure is clothing…
P.S. Nobody has other ideas for a value for R ??? Or am I the only guy here with a well enough developed sense of geek humor to run with this?
I'm currently thinking about how to express ideal formulae for the PMI/PWI, but that's going to be sticky. The units won't cancel out as they do in the Fellabaum-Dolman equation, so the output of those formulae will be in odd compound units and will differ greatly from one another. I may be stuck with separate metric and Avoirdupois systems, and resort to a conversion factor between them. Bummer.
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