Backpack Suspension Design

[Nathan C]

There has been a lot of chatter and a bit of ruckus lately about backpack suspension design. I'd like to clear up our position and explain our assertions. This will be a very high level discussion of how different backpack designs perform when carrying loads over 60 lbs.

INTERNAL FRAME:

Internal frame packs were first developed by Greg Lowe in 1967.

I have asserted that traditional internal frames are not designed to carry heavy loads comfortably. To understand why, we need to conceptualize what is happening with that frame system while at rest and while loaded.



This is a simplified version of a traditional internal frame with hipbelt. Notice the wedge shape to the backpack stays, and how they terminate in the back - or lumbar region - of the hipbelt.

When loaded heavily, this wedge shaped frame transfers all the weight to a narrow region on the belt, tending to cause deformation as seen below.



I have experienced this extensively with backpacks in the past. Before developing the Paradox frame system I owned 25 or more high end backpacks chasing a load hauling platform that performed the way I wanted, and I finally came to realize that it didn't exist.

The problem with this design is the load transfer via two narrow points to a single area on the belt, causing the tendency of the belt to deform and slip down. That deformation will continue until the downward force reaches equilibrium.

Equilibrium in this case is gained when the downward force is equaled by the upward force of the lumbar pad resting on the glutes, and by the lift of the belt hanging off the hips. This is very evident in the side profile sketch above.

These forces can cause massive discomfort. In order to keep the belt from slipping downward I am forced to continually tighten the hipbelt. Over time the belt slips, forcing me to adjust and tighten it again.

The deformation in the belt causes another issue. Because the frame has slipped down your back the torso adjustment is now too short for you. So you either need to tough it out and carry more weight on your shoulders, or you need to adjust the torso for different pack weights.

In a worst case example the result of carrying a heavy load with this pack design is bruised hips, limited leg lift due to the belt riding lower than it should, constant fidgeting and adjusting of the pack, and sore shoulders from a lack of shoulder lift.

ANATOMY:

People claim that pack fit and hipbelt design is a personal preference based on anatomical differences.

Well, it is and it isn't.

If you are blessed with a deep lumbar curve and/or large glutes then the internal frame diagrammed above can work just fine for you at large loads.

How? Because the downward force of the load reaches equilibrium on the lumbar shelf much sooner than it does for someone who doesn't have a deep lumbar curve.

We will touch on anatomy again after talking about the Paradox Frame

[Nathan C]

PARADOX FRAME:

The Paradox Evolution frame system turns the internal frame on its' head.....literally.

Instead of being shaped like a wedge, the Evo is shaped roughly like a triangle.



Because of this shape a large load placed on the frame is spread out over a much larger area, limiting the opportunity for hipbelt deformation.



ANATOMY:

I said regarding anatomy previously that backpack design and hipbelt preference both is and isn't dependent on anatomical differences.

It IS because if you have a deep lumbar then a traditional internal can work OK for you at heavy loads.

It ISN'T because the Paradox frame removes anatomy from the equation entirely. This frame works for ALL back profiles. It's not about anatomy, it's about physics.

[Nathan C]

INTERNAL FRAME HIPBELTS:

Internal frame hipbelts typically have a lumbar pad, and a belt that passes behind the lumbar pad and then around your body.

Why are they designed this way?

Simply put, because if the lumbar pad wasn't there then the ends of the stays would dig into your back. That is the main purpose of a lumbar pad. A secondary purpose of the lumbar pad is to act as a fulcrum. As the pack is loaded and the belt deforms and slides down your back, a large lumbar pad can help the load reach equilibrium and stop the slide sooner.

In short, the lumbar pad is a bandaid developed to address a design deficiency of the internal frame.

The lumbar pad solves some of the issues the internal design has, but it creates another unintended problem.

The area where the hipbelt passes behind the lumbar pad creates a void space where the belt does not make contact with your body. This limits the amount of grip the belt can get, which can increase the tendency for deformation and slip.

To address the deformation issue, internal frame pack makers have developed more tools such as plastic stiffeners in their belts. These tend to create additional discomfort and hip bruising because while the deformation isn't stopped, more of the load is transferred to the points of the hips instead of to the lumbar.


PARADOX HIPBELT:

The Evolution frame allows us to avoid these issues entirely.

Because our frame is triangle shaped, with a wide load transfer area, and has a solid bottom to the frame that keeps the belt at a static width, the opportunity for belt deformation is negligible.

This allows us to concentrate our efforts on creating a belt that simply does not slip on your body at any weight that is human portable.

The way we found to do this is counter-intuitive to conventional hipbelt design. We built a soft, comfortable, flexible belt that conforms perfectly to your body shape. We attach the belt to the frame in a way that the belt can adapt to your lumbar shape. We added a mechanical advantage closure that makes it very easy and secure to tighten the belt. We shaped the belt to predispose it to gripping the body, and finally we faced the belt with a grippy fabric with an incredible amount of surface area.

That simple paragraph of hipbelt design took us months upon months of work, testing, prototyping, tweaking, many fabric changes, many many foam changes, iterations, stress, and passion.

The result speaks for itself. Our belt DOES NOT SLIP.