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 Post subject: Re:
PostPosted: Sun Apr 27, 2014 1:16 pm 
Old School Hero

Joined: Mon Mar 03, 2014 11:11 pm
Posts: 158
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All seatpost sizes dependent on outer diameter and tube thickness

o.d gauge
753 28.6 0.7/0.5sb
731 os race 28.6 0.8/0.5sb
708 28.6 0.9/0.6sb
653 28.6 0.7/0.5sb
531c 28.6 0.8/0.5 sb
531st 28.6 1.0/0.7sb
525 28.6 0.9/0.6sb
525os 28.6 0.9/0.6sb
501 28.6 0.9/0.6sb
500 28.6 1.0
531 all terrain 28.6 1.0/0.7sb
531 magnum 31.75 1.0/0.7sb
501 all terrain 28.6 1.0/0.7sb
501 magnum 31.75 1.0/0.7sb
500all terrain 28.6 1.0/0.7sb
500 magnum 31.75 1.0


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 Post subject: Re:
PostPosted: Sat Feb 11, 2017 2:58 pm 
Newbie

Joined: Sat Feb 11, 2017 2:53 pm
Posts: 5
On hand built frame it depends who reamed (bored out) the seat tube, I have only done this once on a 631 tubed frame I built, it came in around 26.8 and the inside of the tube is not perfectly smooth so needs to be reamed out smooth to what ever size you want (within reason) I went for 27.2 using a hand reaming tool, bloody hard work.
cheers


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PostPosted: Sat Feb 11, 2017 5:58 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 10216
Location: New Forest, UK
One other point to consider is heat distortion. High heat during brazing can ovalise the seat tube.
Tony Oliver in his book explains that a meticulously-built frame will take a 27.4 post where a carelessly built one may have either a 27.2 or worse. Reaming thins the walls and is clearly undesirable.


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 Post subject: Re:
PostPosted: Sat Feb 11, 2017 6:11 pm 
Newbie

Joined: Sat Feb 11, 2017 2:53 pm
Posts: 5
Im pretty sure all frames are reamed to a certain extent, the inside of the tubes is not perfectly smooth after manufacture, or at least that's how it was explained to me on the frame building course I took, we certainly didn't try any seat posts before reaming and the tubes did not ovalise, also I would imagine the tubes can be thinner in the area the seat post is in with out loosing strength


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PostPosted: Sun Feb 12, 2017 9:38 am 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 10216
Location: New Forest, UK
We are talking of ovalisation of 0.1mm, small but enough to step down a seatpost size. There is a big difference between a quick lick with a reamer to tidy up and correcting a distorted tube. Remember 0.1mm is only 0.25% distorted.


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 Post subject: Re:
PostPosted: Wed Sep 16, 2020 8:09 am 
Dirt Disciple

Joined: Tue Feb 16, 2010 1:17 pm
Posts: 23
Location: peak district
My 1964 Reynolds 531 frame falcon road bike takes a 26.6 seat post
I have a 1980s falcon 501 frame and it takes something slightly smaller but can’t find a seat post for it


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 Post subject: Re: Re:
PostPosted: Wed Sep 16, 2020 8:21 am 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 10216
Location: New Forest, UK
Wikey wrote:
My 1964 Reynolds 531 frame falcon road bike takes a 26.6 seat post
I have a 1980s falcon 501 frame and it takes something slightly smaller but can’t find a seat post for it


26.2 for example is quite a tricky size to find, try a USE post plus shims. It works fine, run my tourer like this for 15 years.


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 Post subject: Re:
PostPosted: Wed Sep 16, 2020 9:03 am 
Dirt Disciple

Joined: Tue Feb 16, 2010 1:17 pm
Posts: 23
Location: peak district
Thanks for reply
Will have a search


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 Post subject: Re: Re:
PostPosted: Wed Sep 16, 2020 11:13 am 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
Posts: 10216
Location: New Forest, UK
Wikey wrote:
My 1964 Reynolds 531 frame falcon road bike takes a 26.6 seat post
I have a 1980s falcon 501 frame and it takes something slightly smaller but can’t find a seat post for it


Try a really good old fashioned shop. They should have the conical gauge to measure seatpost size for frames.


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