Originally Posted by revelo

Top tier for heavy loads is Thorn, whose rear rack weighs 850g and is rated to carry 60kg when attached with 6mm bolts or 40kg with 5mm bolts. You'll probably have to buy a Thorn frame to get support for 6mm bolts, however. The sturdiest Tubus rear rack weighs weighs 610g and is rated to carry 40kg max. Surly rear rack weighs 1110g and is rated to carry 36kg max. Not that it matters to the OP, since he isn't interested in paying top dollar. Of course, the weight ratings are by the manufacturers, so you can't really rely on them for comparisons. However, there is no doubt in my mind that the Thorn rear rack with 6mm bolts is the sturdiest of the 3 rear racks listed. It's also the widest at the top, and has no front lip to get in the way, and thus is best for duffle bags (for foam pads and synthetic sleeping bags and other lightweight but bulky items) attached lengthwise to the top of the rack.

Obviously, 60kg is an enormous load for the rear rack alone. BUT, capacities should be reduced by 50% if traveling on rugged dirt roads with washboarding, which causes thousands of bounces per day, which will destroy racks very quickly if they are too heavily loaded. So now the max capacity of the Thorn racks is only 30kg, which isn't that much for us desert travelers hauling 20L of water, 7kg of food, camping gear for sub-freezing temperatures, a full repair kit including spare tire, etc, even if we split the load between front and rear racks. The Tubus and Surly capacities should also be reduced by 50% for rugged roads, down to 20kg or so, and that isn't much at all.