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[pct-l] packs: comfort vs weight: Why packs work

thanks for that great info!!  Good stuff.  However, if your entire 
pack weight is ten lbs, a 3.5 lb pack is still a little too heavy.

> Now that everybody has voiced their opinion of which pack is best,
> I'll present some facts.
> 1. The HIP Belt
> The big improvement in packs was Dick Kelty's invention of the hip
> belt. Although there are other ways to relieve weight on the
> shoulders including seriously reducing pack weight, the goal of
> the hip belt -- to transfer the load from the shoulders to the
> pelvis -- is what makes carrying heavy loads possible.
> An ideal hip belt will transfer 100% of the weight to the
> centerline of the pelvic bone. Take your thumbs and press them
> into your waist at the hip line right in the middle of your body.
> That is where you want 100% of the weight to rest. If the weight
> is behind the center point of the pelvis then the pressure will
> rotate the pelvis [your a$$ rotates towards your private parts]
> causing some degree of fatigue and discomfort. Probably the most
> perfect hip belt is the Jansport swingarm system. In this old
> external design a metal [later plastic] horizonal arm connected
> the pack frame to the exact centerline of the pelvis. Other old
> designs included the A-16 and Stephenson wraparound designs where
> the pack frame actually wraps around the pelvic bone to deliver
> the weight to the pelvic centerline. A very simple design was use
> by Kelty in his Tioga. A strap extended up from the end of the
> pack frame to the pelvic centerline on the hipbelt.
> Given the above geometery, lets examine some modern hipbelt
> designs. 1-Dual half belts.
> This is a weight saving approach. Straps are sewn to the pack bag
> to create a "hip belt". As a result the weight is transfered from
> the shoulders to the A$$. The pelvic bone is under constant
> rotational pressure. However, a very lightweight pack can be built
> in this manner, witness Glen Van Peski's half-pound packs and many
> homemade packs. In my opinion the effectiveness of this design is
> based on how much pelvic rotational pressure one can stand. Based
> on talking to many thruhikers, the average maximum is less than 20
> pounds. If the load goes over this, the solutiuon is to tighten
> the shoulder straps, relieving pressure on the A$$. Additionally,
> the average maximum weight that is tolerable decreases with time.
> A hiker may start out with loose shoulder straps but end the day
> with very tight straps and even the waist belt unbuckled.
> The good news is that the total load is typically reduced by 4-6
> pounds. Not trivial.
> 2-Separate Hip belt
> The goal of a separate hip belt is to wrap snugly around the
> waist, then have the weight spread across the back as much as
> possible. Almost all high quality packs [Dana for example] use
> this approach. Manufacturers have become quite creative at
> desinging milti-layer belts with space-age foam materials to see
> that the hip belt wraps snugly around the waist and spreads the
> weight as evenly as possible. A variety of lumbar pads try to keep
> the A$$ comfortable while very extensive shoulder strap systems
> make transfering the weight to the shoulders less tiring.
> Additional, stabilizing straps run from the pack to the pevvic
> centerline on the hip belt like the old tioga.
> A new design by Kelty seems to work well on people with straight
> hips. The Kelty Cloud hip belt is stiff. It won't flex very much
> at all [making it unsuitable for a woman's curved hips] this
> approximating the Jansport swingarm system while space-age
> elastomer foam hugs the hips.
> It should be clear that all this cleaver design is to overcome the
> geometery that says the weight is on the a$$. In fact, the
> designers have been reasonably successful. Women, who typically
> can't find a proper fitting external frame pack, tend to favor
> this type of pack. Still, for straight trail walking, this design
> is inherently inferior to the old externals and internal frame
> packs don't save weight over external frames. The general rule is
> that comparing external and internal frame packs, for a given
> weight and comfortable, 30% of the weight should be carried on the
> shoulders of an internal frame pack wearer. To some this is no
> problem at all. To other it is very uncomfortable.
> My personal experiences:
> One solution I tried was to use was to combine an external pack
> frame with a lightweight pack bag. I simply stripped the old
> codura pack off a Jansport Yosemite and created a lightweight
> replacement. This saved 2.5 pounds. The resultant external frame
> pack was 3.5 pounds and carried better than any commercial
> internal frame pack [Ladies: this may not be true for you, but
> then it may]. Since old Jansport D3, D-5, Yosemite and other packs
> that used the swingarm suspension are available at garage sales
> for cheap, I believe that this is an approach for someone going
> not ultra-light. You may also be able to find the old A-16 frame
> and belt.
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