GETTING THE RIGHT FIT
Fitting a daypack is pretty straightforward, which is why many of them come in only one size. The shoulder straps should wrap comfortably around your shoulders, without pinching or digging under your armpits, and the hipbelt (usually just a length of webbing) should snug the bottom of the pack against your lumbar region to eliminate sway or thumping as you walk.
Multi-Day External and Internal Frame Packs
With bigger internal and external frame packs, fit is a key issue--the most important one you'll face. Fit is all about the "suspension system," which is the part of the pack responsible for bearing the weight and connecting it to your body: the shoulder straps, the hipbelt, the frame, the back padding, and the lumbar area. There are three types of suspension systems:
Fixed Suspensions: Although they have no adjustability, fixed suspensions often come in a variety of torso lengths to accommodate different sized people. The main advantage of a fixed suspension is that, with fewer moving parts, there's a very solid connection between the wearer and the pack, which translates to stability. Downside: Make sure the pack fits you perfectly, because there's no wiggle room.
Adjustable Suspensions: This system has a shoulder yoke that moves up or down a track in the center of the back panel. This lets you shorten or lengthen the space between the shoulders and hips to fit a wide variety of body types. It also gives you the ability to change the way your pack fits if you develop sore spots.
Interchangeable Suspensions: This system has perhaps the best of both worlds. Some companies offer the ability to customize a pack by buying different size hipbelts and shoulder straps. This works particularly well for people who fall outside the range of "average" height and weight.