M How Packs Work
by David Chenault
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The modern backpack performs a simple function in a necessarily multi-faceted way. Beyond holding a given amount of gear, the job of a backpack can be, as Ryan Jordan wrote in Quantitative Analysis of Backpack Suspension Performance "...distilled into two core functions: the transfer of load between shoulders and hips, and the distribution of the load throughout the harness." That a backpack will succeed if it carries the desired load, enables load transfer between shoulders and hips, and does so without causing discomfort (e.g. chaffing, pinching), is not in question. What is still in question, 45 years since Greg Lowe invented internal frame backpacks, is how to best achieve those ends. This article will examine two contemporary frameless backpacks of approximately equal size, the GoLite Jam 50 and the Mountain Hardwear Thruway, in an attempt to detail the design elements that enable a back to function properly, as well as elucidate why these various elements may succeed or fail. To succeed a pack must carry the required load without excessive torso collapse, must do so while being comfortable for days on end, and must provide useable and durable features. The following investigation will examine the Jam and Thruway in all of these areas.
There has been an intriguing evolution amongst ultralight packs over the past decade, and the Jam, perhaps the most influential ultralight pack of the last decade, can reveal a lot about this trend. The Jam shares a grandparent with most other ultralight packs; the Ray-Way rucksack advocated by rock climbing pioneer and backpacking iconoclast Ray Jardine in Beyond Backpacking (1999). The commercially produced father of the Jam, the Golite Breeze, was a truly frameless pack, which is to say it lacked even a sleeve for containing and lending structure to a folded piece of closed cell foam. As the Breeze evolved into the Jam, and the Jam has aged, it has gotten more complex, and almost necessarily, heavier. First came the pad sleeve, along with a hipbelt, then hipbelt pockets, a padded hipbelt, 3D mesh padding on the backpanel, and most recently a revised hipbelt and load lifters. As discussed below, Golite has attempted to keep weight down in the face of feature creep, but the Jam has nonetheless gained 11 ounces in a decade. As shown in the chart below, it is a matter of disagreement whether these changes have resulted in better load carrying characteristics.
- Introduction: The Jam at a Crossroads
- Part 1: The Problem of Torso Length
- Part 2: It's a bag with straps, but not merely a bag with straps
- Conclusion: Why these packs worked
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