Originally Posted by
seenloitering
WalksOn2Wheels,
If you haven't decided on a backpack yet, or if anyone else is considering doing this, make sure you get a pack that allows air to flow across your back. The other trick is that the maximum height of the backpack is different on the bike because your head is tilted back - particularly a problem if you're wearing a helmet. I would also recommend getting a backpack whose dimensions are within the average dimensions for carry-on luggage. Get a pack with a removable hip belt, and if at all possible, sit on your bike with the full pack before you buy it.
The biggest problem, I've found, is that backpacks are designed for an upright back. Specifically, the weight is supposed to rest on your hips via the hip belt, but as soon as you get on a bike, that stops working. Adopting a more upright posture can improve comfort somewhat, as long as your back remains curved enough to adsorb road shock, but I haven't figured out a way to get the weight off my back and onto my hips.
I hear you on all points. I've been commuting with the Osprey Talon 22 for months now, and it's been great. No backpack is going to be perfect in the sweat department, but I sweat anyways, so I tend to ignore it.
Regarding the hip belt, I tend to position my pack a little higher for on the bike than I would my other pack for actual backpacking. And when the hip belt is cinched, the shoulders are slack while standing so that it takes up the slack when I lean over. This works pretty well for me and I don't have any shoulder isues carrying around a 10-15 pound load every day. Maybe more on some days when i have papers to grade.