Confused about seatpost diameters

For some reason, I was under the impression that any given tubeset ( regardless of who built the bike ) all had a common seatpost diameter. Thing is I have bikes built on an early 531 and now a 653 tubeset ( which consists of uber-thin 531 main tubes with 731 stays ), neither of which seem to want to accept what I thought was the standard for those particular Reynolds tubesets: a 27.2 diam seatpost.

Have I just got my facts wrong?

Pluck

Both of my 531 bikes take 26.4 seatposts. Or did, as the eagle is fucked and now takes a 26.. There are several 531 tubesets though though. And my bikes are the cheap ones. .

older 531 and 753 (early 80s) are 27.0, as is Tange Mangaloy

I always though that 531 was always 27.2mm

Well the diameter of the top of the seatpost can change - The previous owner may have tried to wedge in a larger seatpost, or stuck a smaller one in and overtightened the clamp...

'butted' or 'straight walled'. Butting at bb, so thinner giving bigger seatpost. Both my bikes are straight walled so not. And the fucked one is oval, causing the problems..

Given that the builder could ream it to any size they wanted, the idea that tube set X is seatpost diameter Y is at best a little floored.

Given that the builder could ream it to any size they wanted, the idea that tube set X is seatpost diameter Y is at best a little floored.

Your premise is a little floored. Both my Reynolds tubesets have seatpost diameters smaller than I had somehow ended up believing they would be. Unless your builder is able to ream material back into the tube, rather than take it away.

Your premise is a little floored. Both my Reynolds tubesets have seatpost diameters smaller than I had somehow ended up believing they would be. Unless your builder is able to ream material back into the tube, rather than take it away.

I wasn't talking about your ridiculous notion that 531 is always 27.2 I was saying that the idea that a tubeset always takes the same diameter seatpost is wrong as it can be made to whatever size the tubeset can be machined to.

but whilst you brought it up a butted section of 531 may be well below 26mm internal, so if cut at that point the builder would not have to 'ream material back into the tube' as you put it.

Your original notion that 531 is always 27.2 was wrong, except it, understand the reasoning, and go back to whatever you where doing last week before you discovered 'fixies'

Okay, forget the commonly held belief that all 531 frames use a 27.2mm seatpin.

Reynolds 531, right from the 1930s, could be specified with different gauge tubes of plain gauge, single butted or double butted, depending on the frame-builder's preference and the size and purpose of the frame. Seat tubes were usually single butted even when the other two main tubes were double butted. Also, it was common practice to ream out the seat tube for a perfect fit because the tubes could distort slightly during the brazing process.

As such you can get 531 frames with seatpin diameters of 26.6, 28.8, 27.0 and 27.2mm. Also, a frame with, say, a 26.8mm seatpin does not imply that it is not as light as one with a 27.2mm seatpin.

Not sure if this clarifies or confuses matters...

Okay, forget the commonly held belief that all 531 frames use a 27.2mm seatpin.

Reynolds 531, right from the 1930s, could be specified with different gauge tubes of plain gauge, single butted or double butted, depending on the frame-builder's preference and the size and purpose of the frame. Seat tubes were usually single butted even when the other two main tubes were double butted. Also, it was common practice to ream out the seat tube for a perfect fit because the tubes could distort slightly during the brazing process.

As such you can get 531 frames with seatpin diameters of 26.6, 28.8, 27.0 and 27.2mm. Also, a frame with, say, a 26.8mm seatpin does not imply that it is not as light as one with a 27.2mm seatpin.

Not sure if this clarifies or confuses matters...

Clarifies perfectly - thank you.

Pluck

can I just say, seeing as Platini hasn't arrived, it's "flawed". Thanks.