Frame stiffness?

[TXCO]

How much flex is too much? I was recently playing around with my old REI pack and noticed I could give it a pretty good bend. I was planning on keeping it around as a backup for some loads (50-90) but am now pretty concerned. It carried decent in my younger years. Thoughts?

 

[NVCHUKAR]

Depends if it's horizontal flex or vertical. If it flexes when you push down on the pack then it will not carry heavy loads well.

 

[hammer0419]

For years I have used Kifaru pack and they don't come any stiffer. Carry loads like no ones business. I just received my new Exo Mountain 3500 pack. It is extremely stiff vertically so heavy loads carry well. However, it does slightly flex left to right (kind of twists). It creates a VERY comfortable carry! You do not feel like you are strapped to a board.