Re: [pct-l] Pack capacity for PCT truhike

[reynolds@ilan.com]

To everyone who knows pack theory: Please skip this. [My opinion is at the
end]

I followed this, and other, threads about lightweight packs with interest.
I thought it would be good to regurgitate how packs work and why.

Conventional wisdom holds that carrying weight on your hips over the center
of gravity of your body is more effective than carrying weight on your
pack.

If you look at the average [male] back and try to draw a line down the
center of the body [looking from the side] you will see that the area
across the shoulders is well forward of the area behind the small of the
back [To some extent we are all hunchbacked]. It is this area [From the
shoulder line to down six (6) inches] that is closest to *over* the body's
center of gravity.  The external frame of my old Jansport pack is shaped
like a dogleg. The upper portion is a full two (2) inches in front [to the
left looking from the side of the pack]

Jansport [and the old Stephenson and Adventure 16] goes a bit further and
wraps the metal frame around the hips attaching at the center point [in
line with the body's center of gravity] of the hips. [In reality, the new
Jansport uses plastic fingers to do this but the result is the same] The
goal is to place the weight as close to the center line of the body as is
possible. This means loading the heavier stuff in the top compartment as
close to the back as possible. The test of a well loaded pack is that you
can *walk on level ground* with the shoulder straps removed.

The Kelty Tioga [and copies. Almost all packs except the ones mentioned
above are copies.] had a curved frame. The frame curves 1-2" from the
bottom to the top.  Heavy stuff is to be loaded in top of the sack or under
the flap. The Kelty wasn't as efficient as the Jansport. A good pack should
rest on the back while standing without help of the shoulder straps.

My wife has an internal frame pack, called "Natural Balance", that solves
this problem another way. It has two pouchs that are supported from the hip
belt *in front of the pack*. This causes the pack to balance and, in
theory, keep the pack from bulling back and keep from using the shoulders.

Traditional internal frame packs have internal stays that take the place of
the old external frame. Proper fitting entails shaping the internal stay
into an "S" curve that fits the individuals back. Again, the goal is to
create an area across the shoulders that is directly above the body's
centerline. The advantage of an internal frame pack is the adjustability of
the shape. In theory, one can push, pull, bend and manipulate the stays to
conform to your pack perfectly.

For a man walking down a trail, the external frame is almost always better.
For off-trail, skiing, climbing and other activities that require balance,
the internal frame pack is almost always better. This is because the
internal frame pack carries the weight lower so your center of gravity is
lower but the pack weight is not as close to the body's centerline.
Typically women prefer internal frame packs because the external frame
packs were designed for a man's body.

If you remove the internal frame from a pack you have a rucksack. The pack
hanges from the shoulders. The goal of the stay is to support the pack UP
from the hip belt as opposed to hang DOWN from the shoulders. [The Jansport
I have illustrates this perfectly. The entire pack hangs down from the
frame. You could place 100 pounds on top of the pack, and have the rest of
the pack empty, and carry it easily without the shoulder straps.]

Testing how an external frame pack works is very simple. The shoulder
straps are supposed to go from the shoulder *up towards the pack at a 45
degree angle. NO weight is supposed to be on the shoulders. A perfectly
adjusted internal frame pack will have 30% weight on the shoulders and 70%
on the hips.

My Opinion.
I believe that the best packs EVER built for walking down the trail were
the Jansport swingarm, Adventure 16 and the Stephenson wraparound packs.
Only the Jansport is currently available new. I would find one of these
packs at a garage sale, purchase a new hip belt and sew a new bag from one
of these bag replacement kits. Even for women, I would find a Jansport D-5
[4'-8" to 5'-8"] and referbish it.

As a second choice, I would purchase a current Jansport swingarm pack.

However, the TALL Jansport weighs almost 6 pounds while the small Jansport
weighs almost 5 pounds with their standard bag. A custom bag, that is
smaller and lighter, that occupies only the sweet spot across the shoulders
would likely drop the weight to 4 pounds. Keeping the weight on top of the
horizonal part of the frame [behind the head] or below it [across the back]
would allow you to make more miles a day, even if the pack was a pound or
so heavier.

As a third choice I would get a Kelty Tioga from a garage sale and retrofit
the bag using lighter nylon.



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