In a message dated 5/18/03 8:32:49 AM Pacific Daylight Time, kctommy@msn.com writes:
> Does this mean that Columbus seat tubes at one time took smaller seat posts
> than the 27.2 for SL and 27.0 for SP bikes? When did the change from
> smaller diameter tubes take place?
If you measure unbrazed tubes, SL will fit 27.4 and SP will fit 27.2. When
brazed, due to distortion, SL fits as 27.2 and SP fits as either 26.8 or
27.0, depending on the manufacturer and how they finished that particular
frame. I have similar vintage SP Bianchis (60s) that are 26.8 and 27.0. The
tubing gauge of the main tubes for SL is .9 x .6mm, for SP it is 1.0 x .7mm.
This has not changed over the years.
Stevan Thomas
Alameda, CA