Seat post sizing problem

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snibgo
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Joined: 29 Jun 2010, 4:45am

Re: Seat post sizing problem

Postby snibgo » 20 May 2011, 4:29am

Thanks for that, Greg. Interesting stuff.

I always understood the difference between 531C ("competition") and 531ST ("special tourist") was wall thickness, with C being lighter for performance and ST being heavier for knockability.

I hadn't encountered the silver/brass brazing distinction. I suppose there might also be an age problem, with corrosion reducing the internal diameter of the downtube.

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Mick F
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Location: Tamar Valley, Cornwall

Re: Seat post sizing problem

Postby Mick F » 20 May 2011, 7:51am

Very interesting, thank you.

I've just dug out the original catalogue I received from Mercian back in 1986 when I ordered my Vincitore.

Description of all but a couple of their frames says:
Seat Pillar Size - 27.2mm (not included)

The 753 Special has a choice of 27.0mm and 27.2mm

Frames listed:
Tourist Tandem - 531db
Super Tourist Tandem - 531db
Vincitore - 531c
Professional - 531c
Strada Speciale - 531c
Miss Mercian - 531c
753 Special - 753
King of Mercia Touring - 531c
King of Mercia Racing - 531c
Olympic - 531db

There is a Superlight frame that can be "Reynolds Professional" or "Reynolds Special Lightweight" but it doesn't say anything about the seat post.
Mick F. Cornwall

pherron
Posts: 247
Joined: 15 Oct 2007, 7:46pm

Re: Seat post sizing problem

Postby pherron » 20 May 2011, 8:17am

Thanks for all the helpful replies. Some interesting facts and I feel more confident about my seatpost size now.

gregoryoftours
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Joined: 22 May 2011, 7:14pm

Re: Seat post sizing problem

Postby gregoryoftours » 22 May 2011, 8:23pm

I have a 92/3 orange clockwork mtb frame and I had the same thing - the seat tube diameter is said to be 26.8 but a 26.8 post rattled about in it and required far too much torquing down to get it secure. I found that a 27.0 post still fitted without having to twist it from side to side, and the split section at the top of the seatube looked much more healthy when tightened.

pherron
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Joined: 15 Oct 2007, 7:46pm

Re: Seat post sizing problem

Postby pherron » 23 May 2011, 7:58am

Currently operating with a beer can shim and all seems ok.

djsb
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Joined: 25 Jul 2010, 6:06pm

Re: Seat post sizing problem

Postby djsb » 20 Dec 2017, 4:05pm

Hi,
Does anyone know what the standard length of the seatpost is for a Dawes Galaxy. I've had my original seatpost removed after it seized in the frame so I didn't get a chance to measure its length. I've bought a couple of replacement posts (27.0mm and 27.2mm 400mm length) that I intend to shorten.
The frame accepts 18cm of the tube before it gets stuck and there is a 10cm minimum length marked on the new seatposts so I should be ok. The original seatpost suited me fine, it's just that it got stuck. If I knew the original length it would save me some time. Thanks.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Seat post sizing problem

Postby Brucey » 20 Dec 2017, 4:46pm

there is no 'right length'; it depends whether you want to be able to move the saddle up or down in the future or not. So for example if you have 14cm in the frame when the saddle is the right height for you, that leaves +/- 4cm leeway. Cut it 4cm different and you could have 0-8cm of adjustment, all in one direction.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

rjb
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Location: Somerset (originally 60/70's Plymouth)

Re: Seat post sizing problem

Postby rjb » 20 Dec 2017, 5:09pm

The question you should be addressing is why is it getting stuck? If you shine a torch down the seat tube can you see any obstruction? If its corrosion or rust you may be able to clean it up yourself using a broom handle, slotted with a saw and some emery paper wound around it. Bike shops have a reamer for this purpose.
Merry Xmas
At the last count:- Focus Variado, Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin, Raleigh 20, Falcon K2 MTB dropped bar tourer, Longstaff trike conversion on a Falcon corsa. :D

Roadster
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Location: E.Lancs/W.Yorks border

Re: Seat post sizing problem

Postby Roadster » 21 Dec 2017, 2:36pm

I don't know why some people are dismissing the very idea of seatpost diameters other than 27.2: my 1983 Holdsworth Mistral tourer has 531ST tubing throughout and came factory-fitted with a 27.0mm seatpost. However, I have never heard of any size other than 27.0 and 27.2 being used with that tubeset.

nsew
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Joined: 14 Dec 2017, 12:38pm

Re: Seat post sizing problem

Postby nsew » 21 Dec 2017, 3:33pm

Roadster wrote:I don't know why some people are dismissing the very idea of seatpost diameters other than 27.2: my 1983 Holdsworth Mistral tourer has 531ST tubing throughout and came factory-fitted with a 27.0mm seatpost. However, I have never heard of any size other than 27.0 and 27.2 being used with that tubeset.



E33B1A0D-F6C7-4066-A24E-F03BAA4353B6.jpeg

nsew
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Joined: 14 Dec 2017, 12:38pm

Re: Seat post sizing problem

Postby nsew » 21 Dec 2017, 4:03pm

Oliver notes in the text of Touring Bikes that there are rare variables in tube wall thicknesses where a size smaller seat pillar is required. And also that seat pillars can vary in as much as 0.2mm.

nsew
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Joined: 14 Dec 2017, 12:38pm

Re: Seat post sizing problem

Postby nsew » 21 Dec 2017, 8:33pm

edit

Brucey
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Re: Seat post sizing problem

Postby Brucey » 21 Dec 2017, 9:06pm

FWIW plenty of 531ST framesets accept a 26.4mm seat pin.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

nsew
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Joined: 14 Dec 2017, 12:38pm

Re: Seat post sizing problem

Postby nsew » 21 Dec 2017, 9:42pm

Would they be European metric?

Brucey
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Re: Seat post sizing problem

Postby Brucey » 21 Dec 2017, 9:52pm

nsew wrote:Would they be European metric?


no, they offered different seat tube specifications, intended for larger/stiffer framesets. They may have started to do this after Tony Oliver's book was published.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~