I've been building interesting custom racks, and it's time to highlight a few. In a world where sturdy aftermarket racks are readily available, having a custom rack built for your bike might be viewed as something of an indulgence. When you get down into the details, however, you'll find that a custom rack is a much different beast. Being designed to mate exactly with your frame's mounting points, a custom rack eliminates the clutter of bolt-on adjustable struts found on "universal fit" racks. Clean looks, lower weight and fewer fasteners to possibly come loose. Among my customers, however, the compelling reason for a custom rack seems to be the availability of an infinite variety of dimensions and configurations, and the ability to have all of the "bells and whistles" (light mounts, wire guides, fender braces, etc.) that your heart desires. When designed in concert with a new frame/fork, a custom rack can take advantage of braze-on mounting points which otherwise would not have been designed into the frame/fork
The photo above is of a 3-piece modular rack system, with a small fixed top rack and two detachable lowrider pannier frames. This rack system was designed to go with the low-trail fork in the photo, and the pannier frames attach quickly using three M5 bolts each. The top rack is a little wider than common, which allows the crown struts to fly around the new V-O Grand Cru standard reach dual pivot caliper brake, and provides better triangulation to brace the detachable frames' mast. The customer wanted to be able to attach/detach the pannier frames without disturbing the attachment of the top rack, hence the second mid-fork mounting point. Additional views and details may be found in a photo set on my Flickr gallery.
Commercial rear racks typically are dimensioned for the large-footprint trunk bags that all bag vendors seem to make. Gilles Berthoud also makes a beautiful scaled-down trunk bag that's sized just right for your jacket and lunch, but which looks silly when perched atop a full sized rack. The photo above shows a small-format custom rack that was designed specifically for this little Berthoud bag. The rack also has a braze-on for attaching the quick-release bracket for the LED taillight.
And, finally, here's a simple rack designed for a small touring bike. On small frames like this, the shallow angle of the seatstay positions the rack braze-on quite far forward of the rear axle. You still have to position the panniers back far enough to avoid heel strike, and "universal fit" racks end up with very long adjustable struts/straps to span the gap. On this custom rack, the long reach to the seatstay is still present, but the span now is integrated into the rack's basic structure. With a comparable capability, this steel rack weighs about 2/3 of the aluminum rack (plus steel fittings!) that it replaced. And it looks so much nicer, too.
All of my custom racks are fillet brazed using thin-wall, aircraft grade 4130 CrMo steel tube.