I really, really wanted to come here and give this a 4 or even 5 star review, but it's just not there yet, and it could be with some engineering adjustments. The Ibera PakRak is a great idea. Taking the load off the back's of bike-commuters and light tourers with a simple seat post mount rack and a well made clip to secure bag is fantastic in theory, but the execution is where this fails. Now, I ride a size small (50cm) cyclocross bike, so your experience may differ based on size and geometry, but I would think this should work just as well in my situation as it would most road bikes. With that size and form-factor in mind, I have yet to find a comfortable place to mount the PakRak that does not have rubbing or overlap issues. It's great that the rack tray is extendable, but unless you're on a very upright, seat-forward setup, the max-extended option seems like what the minimum extension parameter should be. At the maximum extension, with the rack mounted high, low or in the middle of the post, my saddle hits/overlaps the bag (removing some of it's storage capacity in the process) and my inner thigh rubs the seat-post clamp. Thankfully for me, my commute is less than 5 miles, so for now I can put up with it, but I'm looking at a means to modify this as to avoid at the very least the rubbing problem. Rubbing will eventually wear away at my clothing, and that's a show-stopper. I've tried this on two other bikes I own, and it looks to have the same issues, because of my bike fit. I'd love to see them improve the rack design, as the bag conversely is a 4.5 out of 5 star item. The worst bit about it is it's best feature: the faux-carbon fiber solid floor casing. The carbon fiber material looks tacky, I get asked about it a few times a week, but the security the hard plastic form provides is great, and pulling it on and off the bike is a breeze (as long as I get the front tucked under my saddle OK). The storage capacity is visibly deceiving, in a positive way. With the extra pockets you can easily pack a day's clothes, a snack or two, shoes, bikes tools and a tube without a problem. You're not going to comfortably squeeze a laptop in here, but an iPad or other 10" tablet isn't out of the question by any means. And it's light, which is good considering you'll be filling it with your heavy wears every day and pakrak'ing it across town.

------ Update/Edit (9/23/2016) - Let's add another star ------
So, now at well over 300 miles commuted with this bit of kit, and I can honestly say I've come to really like it. I complained abut the rubbing and the fit on my smaller bike, but after some fit adjustments I've got it dialed into to a point where I can ride more comfortable without sitting right on top of the pakrak and with minimal or no rubbing. I had to shift my saddle forward and make adjustments to my cleats subtly to get it all comfortable again, but now I can use this thing confidently. It's held up to some of the worst roads around Cleveland, it's climbed up some tough hills and descended a few too, all without a single problem. Sure, it's not perfect, and the amount of stuff it fits is limited, but I think its perfect for your standard city commuter. Attached is a quick photo of it on my bike, fully extended, filled with a camera, flip-flops, hoodie, pants, two shirts, a tube, pump, patch kit and multi-tool and basic toiletries... for scale/reference.

Mounting system and clearance for my bicycle type

I needed more storage for longer rides and wanted something that wasn't cumbersome yet holds a decent amount of stuff. Panniers were a bit overkill for what I needed, and I didn't really want to install a full rack on the back of my bike. This seat post rack & bag was exactly what I was looking for. It installs easily onto the seat post & includes several rubbery inserts for proper fit and to prevent scratching of the post. I recommend tightening it down very well to discourage horizontal swinging when carrying the bike at an angle or setting the bike down on its side.

I have most certainly exceeded the recommended weight amount for this rack & bag on numerous occasions and have yet to have any issues whatsoever. The ability to quickly snap the bag in & out is something I can't imagine not having now. When locking the bike up or mounting it to a car rack it literally takes me about one second to remove or mount this bag to the rack. It's also quite spacious; I've actually been able to fit my Kryptonite New York U-lock, cable lock, Canon 5D Mark III, 2 extra 20 oz water bottles, backup headlight batteries, & at least five Clif bars in this thing all at once. Added weight means added work of course, but having such an option is invaluable. I bring a lightweight yet sturdy black garbage bag with inside in case it rains as the bag on its own is not waterproof. The bottom of the bag is a hardened plastic, allowing it to maintain shape and preventing the bag from becoming wet from ground water spray off the back tire.

The bag & rack on their own are lighter than I expected, an added bonus. I've had no issues with vertical swaying; in fact I prefer the single-point mounting of this rack as it provides a slight bit of added suspension for any expensive items you may be toting with you, like a camera. From simply riding I've yet to have any problems with horizontal swaying, however once again recommend mounting tightly to ensure this. If you take very sharp turns frequently you may want to periodically check the horizontal orientation of the rack; the more weight stuffed into the bag the easier the rack will turn off the desired axis under the bag's weight. Another advantage I've found is that this rack is easier and faster to mount between several bikes than a standard rear-mount bike rack due to it simply attaching to the seat post.

There are large pockets on each side of the bag as well as one smaller pocket on the back. On the back is also a reflective fabric strip which I find particularly useful for clipping on additional rear lights. Reflective fabric also lines this bag on the sides as well. I highly recommend this rack & bag combo.

Pros:
- Hard-shell bottom on the bag
- Quick-clip system takes about one second to attach & remove bag to & from rack
- Capable of holding more weight than the specified maximum without problems
- Reflective striping
- Lightweight on its own
- Rack is easy & quick to install

Cons:
- Possibility of swaying horizontally if filled heavily & rider is taking frequent sharp turns
- If adding lots of additional weight you may want to get a rack with additional attachment points

Putting this on can be a little tricky but once you have it on it is very sturdy and will not move as long as you tighten it up every now and then

It fits great on our new bikes. Great size.