One factor to bear in mind when different seatpost sizes are found on the same model is frame size. Many builders especially the more thinking ones will use a heavier gauge seat tube on the larger frame sizes which will mean a smaller diameter seatpost... Gazelle were particularly adept (at least in the 90s with 531) at picking tubing so much so that their larger frames were actually stiffer than their small ones, quite a feat.
The other factor has to be shop preparation. In the 50s and 60s it was quite rare for shops to ream seat tubes during frame build-up and not many builders used reamers either. So the occasional shop that took a great deal of care reaming a seat tube may have actually arrived at the true seatpost size needed. Some frames quite likely had a distorted out of round seat tube that would only take a seatpost one size smaller... Reynolds 531 DB tubing (with a single butted seat tube of course) in metric size should never need a seatpost smaller than 26.4mm.
Hilary Stone, Bristol, British Isles
Jerome & Elizabeth Moos wrote:
> As I discussed with John offlist, 26.2 was one of the three common post sizes on quality French bikes in the 60's and 70's, the other two being 26.4 and 26.6. I've seen these three with roughly equal frequency, even though most of the bikes were made with metric gauge 531DB. If you look at the Sheldon Brown database someone posted earlier, you will see that for the same French model, PX-10 for example, the post size varied from year to year. In fact I suspect it varied more than that and Sheldon was just listing specific bikes he had seen and their post sizes. I rather imagine what happened was that high volume French makers used all three sizes, maybe in a single day, and which one fit just depended on how much, if at all, the seattube was reamed after the frame was brazed. It's possible different French builders used different gauges of metric 531DB, but that wouldn't explain different post sizes on the same model. The bikes I've seen made from
> quality butted Vitus steel tubing also used one of the above post sizes, but I haven't seen a large enough sample to know if those used one of these sizes more than others.
>
> It does seem from the postings so far that 26.2 was fairly common on Italian bikes, particularly in the 50's and 60's. I don't own a Cinelli, but I've read here that the 26.2 post on what the Cinelli purists consider a "real" Cinelli was dictated by a sleeve that was inserted inside the seatpost. If that is the case, was this a common practice among Italian builders in the 50's or 60's? Or did the common Italian tubesets of the 50's and 60's take a 26.2 post, with Cinelli using the sleeve to maintain what had become a de facto standard Italian post size after they began using 531 or Columbus? For that matter, how far back were what we think of as "standard" and "French" tubeset OD's actually standard? Did other European nations at one time use the tube OD's we now call "French"? And perhaps metric threading as well? If "French" tube OD's were used by the Italians in the 50's and 60's, that might help explain the use of 26.2 seatposts. I know a
> number of CR members own Italian bikes from just after or from before WWII. I'd be really interested to know the tube OD's and the threading of those bikes to eatablish if what we think of as "Italian" standards go back before WWII or if they only developed in the 70's or late 60's.
>
> Regards,
>
> Jerry Moos
> Big Spring, Texas, USA
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> --- On Thu, 12/31/09, Tory Werne <twerne@bellsouth.net> wrote:
>
>> From: Tory Werne <twerne@bellsouth.net>
>> Subject: Re: [CR] 26.2 seatpost size
>> To: "'John Barron'" <john@velostuf.com>, classicrendezvous@bikelist.org
>> Date: Thursday, December 31, 2009, 6:35 AM
>> John:
>> RE: 26.2mm seatpost size
>>
>> You can add to the list
>> 1971 Garlatti Parma, using an external seat collar clamp
>>
>> Tory Werne
>> Woodstock, Georgia USA
>> ---
>>
>>
>> -----Original Message-----
>> From: John Barron [mailto:john@velostuf.com]
>>
>> Sent: Monday, December 28, 2009 3:56 PM
>> To: classicrendezvous@bikelist.org
>> Subject: [CR] 26.2 seatpost size
>>
>>
>> I'm compiling a list of vintage, on-topic bikes that accept
>> a 26.2 mm
>> seatpost.
>>
>> Cinelli is the obvious maker of frames that use 26.2 mm,
>> but please reply
>> with any others that you know of that use this size.
>>
>> Thanks!
>>
>> John Barron
>> Minneapolis MN USA
>> http://www.velostuf.com