Originally Posted by crust & crumb
i've always questioned this piece of seemingly conventional wisdom (which lies interspersed throughout many a bag thread) insofar as: to what degree? for example, i run my bars at saddle height, which by most of your standards would seem to be well classified as "a really upright position". speaking in general terms, of course, am i still within the realm of a shoulder bag here, or is my riding posture sufficiently upright-enough to merit a backpack?
I wouldn't call that (saddle & bars at same height) upright, particularly. Hybrids and comfort bikes and such are upright. Bars usually a couple inches at least above seat, closer as well. For that, yeah, a backpack feels better, cuz the weight is more on your shoulders. My road bike has bars & saddle at same height these days, and I find my mess bags are all fine on it. Ahh...except for the littlest one, which doesn't have a sway strap, but that's cuz it wants to swing around, not cuz it hurts.
I guess the best way to answer your question is to ask you one: does the weight of your pack rest on your back or does it hang on your shoulders?