yeah, but...
a 27.2 seatpost is a touch smaller than 27.2...and tubes are not perfectly round either...
in the real world, those silver-brazed sl and 531c frames _must_ use a 27.4 post for a correct fit and the sp frames _absolutely need_ a 27.2 post for the proper fit. only those are really round, really smooth, really ready for the post.
the fact that most folks get away the slightly undersized posts is more a testament to light riders, lack of grease and the tensile strength of a campag seat binder bolt.
fwiw, i've seen pleny of bent ears on columbus-tubed frames. i've done it myself plenty in the long, long ago. we used to also see it tons on the (off topic! horror!!) custom mountain bike frames we built 25 years ago with sl and sp tubing mixes with down tubes used as oversized top tubes. fun stuff...
'spiney' norman neville still new wavin' in ct
_now_ the lesson is over.
> I'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.
> As an aside, when 853 became available, Reynolds
> specified a 27.2 seatpin for a .8/.5 seattube.
> Presumably the air hardening nature of the 853
> wouldn't allow for the light clean up necessary to
> remove the brazing/ welding distortion even a
> careful skilled builder would cause.
> Another aside- anyone ever wonder what sort of
> seattube Raleigh Internationals used? Didn't they
> take a 26.6 or something? That would indicate (
> with non- metric O.D.'s at least) a .9 or full 1mm
> wall. Double butted seat tube, maybe? And didn't
> Cinelli Corsa B's have a similar size?
>
> Best regards,
> Wes Gadd
> Unionville,CT
> spiney norman <nevilmanyeah@yahoo.com> wrote:
>
> --- MARK wrote:
>
> > I believe Columbus (?) KL tubing used 27.4 posts
> >
> > Mark Hoffman
> > New Britain, CT
>
>
> most handbuilt, silver-brazed columbus sl-tubed
> frames
> actually need a 27.4 seatpost and the same type of
> frame with an sp seat tube take a 27.2 because the
> tube does not ovalize much if at all with the
> careful,
> low-temperature construction. brass-brazed,
> production-type, overcooked frames with sl seat
> tubes
> use a 27.2 and sp a 27.0.
>
> many if not most of the ill-fitting seatpost issues
> with high-end handbuilt columbus sl and sp frames
> come
> from the fact that some builders may not have been
> aware of need for the slightly larger seatpost.
>
> 'spiney' norman neville
> new wavin', ct
>
>
>
>
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