 |  | | | |  | |  |  | TDF seat post size? |  | |  |  | |
 Posted: Thu Dec 10, 2009 10:10 am |
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| trials guy |
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| Joined: 30 Jan 2009 |
| Posts: 75 |
| Location: Woodacre Calif |
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| Sorry to ask a question that has probably been asked several times before but.... What is the diameter of a seatpost on the early '70's Tour de France? Thanks in advance. |
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| Posted: Thu Dec 10, 2009 2:19 pm |
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| edorwart |
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| Joined: 23 Sep 2009 |
| Posts: 50 |
| Location: Bucks County, PA |
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| Should be a 26.4 mm but you may find that a 26.2 or 26.6 may also work depending on how crushed the seat tube is or of there is any paint or corosion inside. |
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| | | | | | | | | Re: TDF seat post size? | | | | | |
| Posted: Thu Dec 10, 2009 7:40 pm |
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| verktyg |
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| Joined: 14 Jan 2007 |
| Posts: 2814 |
| Location: SF Bay Area |
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| trials guy wrote: |
| Sorry to ask a question that has probably been asked several times before but.... What is the diameter of a seatpost on the early '70's Tour de France?. |
As Eric said, the seatpost size can range from 26.2 to 26.6mm.
The standard correct size seatpost for foil decal Super Corsa and Tour de France bikes from the early 70s is 26.4mm.
This is based on 28mm metric diameter Reynolds 531 seat tubes with a wall thickness of 0.7mm at the top of the tube.
28mm - 26.4mm = 1.6mm, divided by 2 = 0.8mm per side which allowed for a 0.1mm slop per side for an easy fit.
Occasionally these bikes came with seat tubes with a 0.6mm wall thickness and 26.6mm would be the correct size seatpost for one of these frames.
Read these messages for more details:
Scroll down to my message at the end of this thread:
http://tinyurl.com/yl5agxd
Also this message in the following thread?:
Conversion - BWG Gage to Inch and MM
http://tinyurl.com/yk6m7es
When checking for the seat tube size. I spread the "ears" on the seat lug if they have been squeezed closed too much. The split in the rear should be equal width, top and bottom.
Seat tubes inside the lugs are frequently out of round and sometimes bulged from the excess heat used to attach the seat stays. It appears that many builders run a reamer down the seat tube before final assembly just to clean out excess paint. they install whatever seat post fits.
I have some tools to drive down the seat tube to round out the lug and remove bulges. This is something that should have been done at the factory but frequently wasn't (all makes of bikes). Next I ream the seat tube in the lug area to the correct size then hone it to remove burrs and provide a smooth inside surface for better grip on the seat post and easy height adjustment.
The last part is try a seat post to make sure it fits smoothly. This is a Campy 26.6mm seat post in a TdF frame.
Hope this helps. |
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_________________
Chas.
SF Bay Area, CA USA
==============
1984 Criterium
1969 TdF
1971 TdF
1974 TdF
1984 TdF x 2 Bikes
1970 SC
1971 SC
1972 SC
1984 SC
1984 Team Pro
1985 Professional
1990s Team Replica |
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