Originally Posted by
obrentharris
Interesting bottom bracket shell; socketed for chain stays but fillet brazed at seat tube and down tube. Is this common on Serottas?
It's actually even more unusual than that. The seat tube and down tube are tapered. They're both 28.6 at the top but around 36 mm at the bottom bracket. I believe this is standard for Serottas of this period (~1987). If I understand correctly, this is the "Colorado Concept" tubing that is (I think) unique to Serottas.