Originally Posted by
denaffen
As I look at those pics, and especially the head tubes, it's striking to me that the 520 and Campione both measure out at 52, and the Bianchi is the smaller feeling of the two.
What I think is not always considered, and it really took me owning my 620 to do so, is that one must factor in a fork's axle to crown height. Due to the 520's touring design, which necessitates large rims (27"s in this case, though 700C normally), large tires,
and room for fenders (vertically), the fork blades are quite long and thus "creep in on" the head tube's overall length/height. It's deceptive, but the math adds up. If that frame ran small racy tires and an appropriate fork, the head tube would be longer. The seat tube, top tube, and upper head lug are all in the same place. This has happened to me when evaluating a frameset that I thought was for 700C wheels, but was really for 650C. The head tube length was massive, good for a 65-66cm bike (hooray!), but the seat tube measured just 60cm or so (horizontal top tube and everything). Enter confusion. Then enter a 700C wheel and deflated 23mm tire that can't even slot fully into the fork's dropouts. Ahhhh, this is a 650C frame. It also explains the 39cm chain stays as well.