Stevan Thomas observes:
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.
First, thanks, that's helpful! Second, it gives me an excuse to remind folks of a bit of good news and bad news about Cinellis:
Good news: Cinellis use a sleeve to line the seat tube for the top 4 cm or so, which necks it down to 26.2 -- enough difference to look a bit odd. But, this means that it is much harder for a post to corrode and seize.
Bad news: harder to determine tubing type.
harvey sachs mcLean va
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