Oh, the joy of data!
I spent a happy half hour comparing tube diameters of my C-16R and my ‘Mystery Frame’. Both frames are 19” measured centre-to-top. Measurements were made with vernier calipers and the resulting diameters include paint thicknesses. All dimensions in millimetres.
Here are my findings:
Orange C-16R
Head Tube 33.2 (plain diameter – no external butting)
Down Tube 31.9
Top Tube 28.8
Seat Tube 32.0 at mid height / 32.9 at top (where externally butted)
Seat Stays 19.2 near top, just below upper curved part
Fork Blades 27.3 just below fork crown
Orange ‘Mystery Frame’
Head Tube 37.5 (between butted ends)
Down Tube 35.4
Top Tube 32.1
Seat Tube 32.1 at mid height / 33.0 at top (where externally butted)
Seat Stays 19.8 near top, just below upper curved part
Fork Blades 29.0 just below fork crown
Whereas the seat tubes appear to be substantially the same (small differences possibly due to differences in paint thickness), clearly, the ‘Mystery Frame’ has a more substantial down tube, top tube and fork blades
If a bird looks like a duck, waddles like a duck, quacks like duck and flies like a duck, it’s probably a duck.
I think my mystery frame is probably an Orange P7.
Any dissenters from that judgement?