Mainly for women's frames where a smaller front wheel is needed to make the geometry possible (or pursuit bikes, but that's a whole different ball game trying to get the front as low as possible to make it as aerodynamic as possible).
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"