In a message dated 3/19/07 3:29:35 PM, wesleygadd@sbcglobal.net writes:
>'ll throw in my two cents here. A typical single butted Columbus SL or
>531 "C" seat tube with an outside diameter of 28.6 mm (1 1/8") and wall
>thickness of .9/.6 mm will have an inside diameter of 27.4mm at the seattube
>end. A 27.2 seatpin slides nicely into an unbrazed , raw seattube. Doing
>the math tells us that the .2 mm difference in diameter amounts to about
>.008", or about .004" radial clearance. I doubt that one could even enter
>a 27.4 mm pin into an unbrazed .9/.6 seattube. I always thought the 27.4
>size was to suit a .8/.5 seattube, or a handy fix for an overzealously
>"prepped" .9/.6 tube.
All this assumes that wall thickness is controlled better than it is. My
experience-going back 30 years-is that an SL seat tube will always take a 27.2
seat post with just the lightest reaming where as a 531 seat tube, nominally the
same at a quoted .6/.9, will fit a 27.2 post slightly loose and a little touch
up reaming will result in a perfect fit for a 27.4 post. I use correct size
reamers, not adjustable. And Waterford must agree with me because their 531-and
753, a different kettle of fish-frames use a 27.4 post.
And there are some on this list whose 531 frames I have reamed to 27.4 who
are much happier with their seat post fit. And again, look at all the crushed
ears on 531 frames versus Columbus frames. You almost never see a crushed ear on
a Columbus frame.
Phil Brown
Thus endeth the lesson in san Rafael, Calif.
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