I got a rack last night, and mounted it to my CX/commuter bike. It's an older model of Planet Bike's KOKO rack, which has lots of mounting points for panniers. I'm well on my way to Fredmobile status.

I noticed the 55 lb max capacity, and hesitated for a minute (how will I carry room-sized aquariums and wrought-iron lawn furniture??), then stopped to think - that's a lot of weight. How much do you actually carry on your commutes, and on other rides? What are your heaviest bring-alongs? That will help me put this number in context, and figure out if I got bamboozled.

Already, I can tell this is a much more convenient way to carry a book. Too bad I waited until it's getting too cold to want to sit on a bench at the park and enjoy one.

Do panniers need to lay flush against a rack? My cassette and RD stick out a bit on the drive side, and the disc brakes stick out a bit on the other side. Seattle's rainy season isn't that far off, and I think the smartest thing would be for me to start bringing a dry set of clothes to work every day.

Finally, should I be worried if the bottom of the rack doesn't attach to the eyelets or the skewer or any of that, but instead clamps to the rear triangle ... similar to how brifters attach to handlebars? The clamps are coated in rubber, so they're grippy, and don't scratch the paint - but is there any reason to think this will let go under load and that the rack might go into the rear wheel? I'm guessing it's fine, but what do I know?

I use Wald folding wire baskets. I easily carry three half gallon containers of milk, quarts of yogurt, apples and canned fizzy water. Oh, and eggs, too.

But for everyday work stuff I still use a messenger bag. It's just easier for me.

I just chain the wrought iron lawn furniture to the back & drag it. Can't help you with the aquarium.

I weighed my backpack one day, fully loaded with change of clothes, towel, hygiene products, U-lock, cable lock, pump, tubes, multi-tool, etc., (I don't travel light) and it was still under 20 pounds. 55 pounds should be far more capacity than you need for commuting.

I have carried a 30lb bag of Dog Chow on the rear rack of my folding bike. I have carried a whole roasting chicken in a pannier on said rack.

55lbs sounds like the load when bolted to the frame. I wouldnt like to load up P-clips with that. My solo touring load for 4 panniers is 55lbs. Most commuting loads are under 20lbs.
I sometimes carry large, heavy loads such as bags of plaster. I wire a short plant across the top for extra support.

Why don't you pack your bag, with what you think you will carry and weigh it?

You can always weigh a case of beer, or a gallon of milk before you load it up.

Besides, the chances of the rack failing if you got to 56 lbs is almost nill.

Learning how to pack it on the rack, now that takes some work as well as experince.

I had the same problem when I got a nice backpack. "What? Only 35 liters? But I can't fit my car in there!" I don't have a lawn - small apartment - so there's no conceivable need to carry lawn furniture around. I think I just get a little nervous with limits ... but it sounds like I would be doing something very unusual if I found myself lugging too much weight around. Which is good news for me!

My car is a 92 Miata. It would easily fit in that backpack.

my eight year old, 55 pounds (or so).

I don't think I get much over 30ish lbs on a regular basis. That's when I buy 2 weeks worth of canned cat food and cat litter. I carried probably closer to 50 when I went on a short tour in June.

Getting weight compact enough to overload a standard rack takes some doing, especially if you're just commuting.

Commuting I don't think I've ever gone over 20 pounds or so. It's tough to say because I don't know how much library books weigh. Hauling books back and forth is an occupational hazard. As for normal commuting stuff--clothes, food and the like--it's certainly under 10 pounds.

Grocery shopping is another situation entirely. It's not unusual to have 10 lbs each of potatoes, onions and rice, then 5 lbs each of apples, oranges and bananas. That's 45 right there before other produce, meats, canned goods, frozen, and whatever else will fit in the panniers. If I had to guess, my max was about 60.

My rack is rated for 40 kg, 88 lbs. I don't know the weight rating of my Arkel Shopper grocery panniers. I haven't reached it yet, though.

Does your cat only eat a single flavor, too?

He's not that picky, actually. It depends somewhat on the brand, and he won't eat chunks of vegetables, but he'll otherwise eat a pretty wide variety of food.

Most I've carried is around 10 pounds.

Now, my work is only a mile or two away, so I'm not carrying the full stock of repair equipment some of the dudes and dudettes here are. But even if I was, a nice set of supplies probably wouldn't be more than 5 pounds altogether. You'll be totally fine with a 55 pound limit for just about everything short of car-replacement grocery shopping and moving to a new place, I'd say.

Groceries tend to be the heaviest loads I get into. I try not to carry more than 30 pounds on the rear rack. And I prefer when it's around 20.