People into light bikes will naturally prefer aluminum racks. But... This is made out of solid steel bar, not tubing. The flat ends are forged, not flattened tube. If the $30 aluminum tube racks are rated at 40 pounds, then this one should be rated over 100 lbs. (A sticker on it says do not use over 20 kilogram, which is 44 lbs. I think.) Not that I or my bike could seriously manage 100 pounds added ... but I have loaded up 50 pounds of lawn fertilizer at times. The short bars that bridge the rack to the stays would have fit better in my case if they were straighter, so I tried to reshape one in a big steel vise, but regardless of what I did the bar only bent slightly and sprung back as soon as the pressure was off. Maybe if I put a three foot pipe on the end it would have bent, but the pressure was already crazy and I thought that was ill advised. :) That is some good steel. The weak points obviously would be the welds, not the bars, but the welds look nice to me. I figure the weight rating has something to do with lawyers. If you load a lot of weight on the rear of a bike, the handling is completely off and squirrelly, and the rack manufacturer would get sued in the case of an accident if he did not recommend against it. 20kg is probably what stands up in court, not what the rack will hold. Since I broke a rack (from metal fatigue at the stays mount), which this one replaces, I was looking for something tough, and this looks like it. Thanks to the first posters that put up such informative pictures. I thought the rack might slip around at the screw joints (many racks are one piece welded), but it doesn't. The whole rack flexes in a springy way if you push hard, but the screw joints do not move around. Just in case, I added some lock washers, which should take up any slack due to winter-summer thermal cycling. The rack already comes with lock nuts, but lock nuts are good mainly because when they become loose they will not rattle looser. Since I had some experience with helping someone with a nice aluminum rack switching from one bike to another, I was aware of how hard it is to adapt to every particular bike. That rack had an array of extra screws and brackets, but it still took some home-made weirdness to make it work on that particular bike. You can see how different the rack fits on my bike as compared to the other pics. I didn't mention in the picture notes that the gripper material under the pipe brackets is a strip of material they use in wood working to keep small pieces of wood from sliding (without a vice) when routing (which is why I have it.) It looks like the same stuff sold as kitchen drawer liner that keeps silverware from sliding around when you open and close the drawers. The smallest pipe brackets (1/2 inch), though sturdy, were a bit too large even after re-bent, which is why I put some plastic pipe as a spacer around the stays. Since, when I find a really good item at a really good price, either the price immediately gets jacked up, or the item disappears never to be seen again, I got two just in case. But I think my bike will give out before this thing does.(And then I'll have a new one for my new bike!) I am more enthusiastic about this item now that I have it then when I ordered it, which is practically a new experience for me. ----> added May 1, 2011 I see pages of reviews after the last time I checked. I read them all (around 50.) Nothing has rattled loose, nothing bent or kinked, no welds gave out, nothing rusted. The rack is as sturdy and durable as I figured -cross my fingers- 2 years ago. When the weather is over 40 degrees here I do my grocery runs two or three times a week on the bike, and the rack gets a lot of flexing because the "milk crate" box is on top, which is a lot of leverage. In colder weather, grocery runs drop down to about once a week. About weekly I carry 2 gallons of milk in the grocery load. I am wondering what a number of people have in mind who say the rack is flimsy, unless it is not the same rack. I have never seen a normal rack (like under $70) that this one doesn't beat the bleep out of for strength. Maybe aluminum is less springy? Or they have no experience with another rack? I do not get why people did not believe that there are NO bolts included that hold the rack to the bike and realistically NO instructions, which I understood from the people that reviewed this even earlier than me. About the first guy that posted left pictures of what you get. (If these are not present in your package, you were shorted, which quite a few later buyers have been.) If you don't already see how you are going to attach the thing from those pictures, and you aren't creative mechanically, or don't want to be, be kind to yourself and don't get involved. Believe it or not I did not buy this thing because it was startling cheap. That was a bonus. Obviously I did not buy it because it was convenient to attach to my bike (check the pictures of the olive green bike.) From the earlier posted pictures, it looked to me that it was made the right way to be strong. Other racks definitely are not. Stiffness and durability are two different things. In person it turned out to be far stronger than I was thinking. It is something like spring steel, not the mild steel you find in rods and bolts. Actually, most people do not need a particularly strong rack for the way they are using it. They are fixated on cheap. Cheap can turn out to be too expensive if you factor in the value of your time. A few people said the bolts stripped easily. If they did, then the bolts I received were different bolts. I wondered why they put such nice bolts in the package when any old bolts would have done as well. ----> added August 27, 2012 I see where the weakest point is now. There are two alternative holes where the rack attaches near to the axle. You will see the width of metal surrounding these holes is extremely narrow. If you use the lower hole, as I needed to, the narrow part of the upper hole becomes a weak point which gets a lot of flexing. One day, back in the spring, as I was loading up the groceries, I noticed the milk crate squirmed uncharacteristically as I shifted around the gallons of milk. Yep, one side of the rack was snapped at the weak point just mentioned. Considering the 5 mile walk back home, it was worth attempting to ride home that way. Surprisingly, it turned out not to be any problem. I have had my bike fall over at times in the couple of years since I installed this rack, so I am reluctant to exclusively blame the break on this design fault of the rack. I replaced the broken side with one of the sides of the back-up I bought at the same time. Short of some dramatically expensive "industrial strength" specialty racks I have seen, this rack remains the strongest you can find. By the way, in the first of these collision and screw-up incidents, every one of the zip ties I initially used, in part, to hold the milk crate to the rack broke instantaneously, so those stainless steel band-style hose clamps should be preferred to, or added to, zip ties. ----> added November 5, 2012 I have at last unraveled the mystery, to me, of the supposedly crappy, easily stripped bolts some people are claiming. Except for the one person who got bolts that were malformed, the problem is something else: These bolts have six sided holes (like Allen set-screws do), perhaps because they "look nicer" or because they can be tightened with greater force than slot heads or Phillips. They require Allen wrenches. (At least that was their name before metric sizes.) (Allen wrenches are just hexagonal cross-section rods with a right angle bend in them for a handle.) People are attempting to tighten these with the usual slot-style screwdriver or a Phillips screwdriver, and this destroys, not the threads, but the hex hole in the heads, and probably ruins the screwdriver forever too. It never occurred to me that people would do something like that. Don't. I going to guess that Chinese or Taiwan Allen wrenches (also called hollow set screw key wrenches) at the chain hardware or auto supply stores or walmart or sears would not be more than two dollars. I don't know because I have several sets over thirty years old laying around. If you know anybody that tinkers, they probably have them too, and you can borrow them. The bolt is metric 5 mm and the hex slot is 5 mm, I know, but the 3/16 inch size of my set fits the head just right. (3/16 is 1/100 inch smaller than 5 mm; barely visible.) In comparison to tightening with a screwdriver or wrench, these bolts are a pleasure. If you decide to replace the bolts anyway (which I grant has merits too) get the ordinary, commonplace, 3/16 diameter by 3/4 long bolts with hex heads (not hex holes), not a screwdriver type head, and avoid the frustration of working with both a screwdriver slipping, as they ALWAYS do, and a wrench simultaneous. But then you will also need two wrenches, one for the head and one for the nut. Another problem people are having. I think, is they aren't tightening up the screws all the way, and the rack is rickety, and seems flimsy. The provided nuts have nylon plastic inserts, so-called lock-nuts. It you have never seen them before, you won't understand them. They can be started without a wrench, but not tightened past a certain point without one. When the plastic starts jamming into the threads, it produces very high friction, making the nut very hard to turn. You cannot tighten them with your fingers, and not with a misused screwdriver slipping and stripping the head on the opposite end either. It is a slow-going PITA to tighten, but this high friction does keep the nuts from progressively loosening and falling off from the constant vibration of a bike. On large enough bolts, this loosening tendency is overcome by tightening the bolts a measured amount with a torque wrench, just the amount needed to stress the metal to provide the right constant squeeze pressure. On small bolts, sufficient stress may be more than the threads or the head can take, so you live with the possibility they can vibrate loose. Ordinary nuts, once they get a little loose, work looser until they vibrate all the way off, and then the bolt drops out too. Lock-nuts don't loosen, because of the high friction, even if they are not snugged down. I personally use lock-washers. (Also called split-ring or spring washers, and other names.) They are thick spring steel and act like the first spiral loop of a strong spring. If you take the nut off, they spring back into shape. I trust them more than lock-nuts, where the nylon plastic is damaged in putting them on.