I have been backpacking for a year now, about a dozen times total. I currently have an REI Flashpack 50 liter. I am thinking about getting the Flashpack 65 liter instead. I love my Flash 50, but on my first multi night trip, I really overloaded it. My guess would be 40 lbs. I like to keep everything inside the pack but was unable to do so on the last trip. On one night trips I would guess that I have about ten-fifteen liters to spare and my pack weighs about 30 lbs. Also, I often bring by boys with me and end up carrying a little more of the share than I should. I guess my question is, is better for comfort, to max out a pack, or have extra room left in the pack. My fear with getting a 65 pack will be that my gear will be too loose inside the pack and make for an uncomfortable hike.
Loc: California (southern)
I have not used that specific pack, but I see that it does have cinch straps so that the pack can be tightened up if you are carrying less than a full load. In comparably equipped packs, I have never had any kind of a problem carrying a less than full load.
I would rather carry a larger pack, partially empty, than an overloaded smaller pack.
Generally, I'd agree that it's better to cinch up a too-large pack than try to overload a too-small pack. However, it's not because of the size of the packbag.
If you look at the specs for most packs, you'll see they give some variant of a "comfort range" that specifies how much weight the pack can carry and still be "comfortable" (for an "average" person, whoever that is.) It's not a perfect, objective system, and not precisely comparable from one company to the next, but it's a starting place.
The larger packs typically have higher load ratings. Yes, the bags are larger - but more critically, the suspension is usually beefier, and it's the suspension that determines the weight-bearing capacity. (In fact, there are some pack frames sold without a pack bag, for carrying heavy loads like firefighting tools, wood, or for hunting. They are all suspension.) Oftentimes, within a line (say, the Osprey Kestrel with which I'm familiar) the suspension design and features will be the same for the entire series, but as the load ratings increase, the hipbelt might be a bit wider or stiffer, and the framesheet might be a bit less flexible or be reinforced by a stay.
So, as you look at larger packs, pay attention mostly to the suspension - especially if you start looking at packs from other manufacturers and other lines from the same manufacturer. I know, from personal experience, that 50 liter packs from Gregory, Granite Gear, Deuter, and Osprey all carry differently with the same gear in the packbag. Within the Osprey line, the Talon, Atmos, Kestrel, Exos, and Aether each carry a bit differently from the other with the same load; each has a different comfort range, and each has a different type of suspension.
So, when shopping for a new pack, it's all about the suspension.
Which reminds me: load distribution also matters. (The OP may already be aware of this; if so, my apologies - I wasn't trying to insult your intelligence.)
Lori's right about loading the packs when you try them on - I'd add to use the actual gear you plan to carry, if possible. (Pick a day when the shop you visit isn't too busy, because you will use up a lot of floor space and their time.) Each pack will probably have some features that will let you arrange your gear a bit differently - generally, loading heavy things into rear pockets will tend to pull the center of gravity back, and into side pockets will affect the side-to-side balance of the load. (Personally, I don't like a lot of pockets, but I do like the rear "corner" pockets on the Kestrel - they expand inward rather than out, and are a great place to isolate my rain gear without affecting the center of gravity.)
Using your actual gear to test-load will reveal pretty quickly any pack eccentricities that affect the fit.
The other thing to note - while I have not used the Flash 50, I have hiked with many who have, and just observing and listening to the folks using them? I don't think I would buy one. I think the 50 or 60 liter volume is too big for the suspension on the pack. It invites packing 30-40 lbs of traditional gear in, when it's better suited to 20-25 lbs of ultralight gear. Most folks in my hiking group have traditional (5 lb tent, 3-4 lb bag, etc) gear and it will all fit. But since the suspension is in no way adjustable, and isn't as stiff or fitted as, say, a Gregory or Granite Gear, the wearer has difficulty carrying the load.
This is why you should try other types of suspension. You may find that a stiffer, more stable, more adjustable pack suits you better. And if you have not been measure, get it done. Fixed frame packs aren't for everyone - they work well for those they fit, but when they don't fit, ugh.
I am on the long side of a "short" pack frame, and the short side of a "normal/medium" - and so I am extremely careful about pack choices. Two of my current backpacks allow me to adjust the shoulder harness in inch increments to better fit my back. Not being able to fine tune the harness to my back has led to some miserable days.
I think that when you have the right pack, one that fits and carries your gear properly, you will experience an AAAAAH moment - a lot of folks I've backpacked with don't seem to realize it's possible to be comfortable with a pack on.
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki
Great catch - I forgot all about mentioning adjustable versus fixed suspensions, and how much of an effect suspension length can have on fit. Fixed length suspensions on the Granite Gear Vapor Trail and Osprey Exos/Atmos made those packs no-go's for me, because they never truly fit properly. "Infinite" adjustablity (position the velcro at any length) versus fixed-increment adjustability was one thing that swung my final decision toward the Kestrel and away from the Granite Gear Escape and Deuter ACT Zero - my perfect length ended up halfway between two of the settings.
Thank you all for the replies. It all sounds like good advice. I like the idea being able to adjust the suspension. I have been measured several times and I am exactly in between a medium and a large. I think my torso measures 19.5 if I remember correctly so in addition to the volume issue, I have the pack size issue. When I initially tried out packs, I did have them weighted to 25 lbs but I had never worn a pack, so I had no point of reference. I have had some days with my Flash 50 where I didn't even know it was on, and others days where it felt like the cross I had to bear. I know longer keep my hydration bladder in the pocket against my back. I could really feel it and was very uncomfortable. Each time I take a trip, I am trying to make notes of what works and what doesn't work.