Go Back  Bike Forums > Bike Forums > Classic & Vintage
Reload this Page >

French Seatpost Slippage

Notices
Classic & Vintage This forum is to discuss the many aspects of classic and vintage bicycles, including musclebikes, lightweights, middleweights, hi-wheelers, bone-shakers, safety bikes and much more.

French Seatpost Slippage

Old 04-25-20, 03:59 PM
  #1  
Revracer
Senior Member
Thread Starter
 
Revracer's Avatar
 
Join Date: Dec 2011
Location: Eastern PA, USA
Posts: 182

Bikes: 1973 Schwinn World Voyageur | Francesco Moser SL | 1984 Ross Utopian | St. Etienne 531 | 1981 Peugeot PK10 | 2015 Cannondale SuperSix | 2012 Felt F65X

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 46 Post(s)
Liked 29 Times in 13 Posts
French Seatpost Slippage

I am currently using a 25.8 seatpost that was squeaking. I applied grease went for a 60 mile ride and found it slipped down almost 2cm. To be fair, the seatpost clamp when tight has no gap. I never had slippage when I had it in dry. I have read about the inconsistency of vintage French bikes regarding seatposts, but curious if any of you have personally fixed this by:

Find a 26.0 seatpost?
How much bigger of a seatpost is likely to fit?
Get a bigger seatpost and lightly sand until it is just right?
Carbon paste?
Anti-seize?
Revracer is offline  
Old 04-25-20, 04:04 PM
  #2  
bikemig 
Senior Member
 
bikemig's Avatar
 
Join Date: Apr 2012
Location: Middle Earth (aka IA)
Posts: 18,119

Bikes: A bunch of old bikes and a few new ones

Mentioned: 155 Post(s)
Tagged: 0 Thread(s)
Quoted: 4965 Post(s)
Liked 1,450 Times in 963 Posts
Is this for your '81 PKN 10? That seatpost size doesn't seem right for that bike.
bikemig is online now  
Old 04-25-20, 04:06 PM
  #3  
jiangshi
OFG in Exile
 
Join Date: Jul 2013
Posts: 1,757
Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 428 Post(s)
Liked 146 Times in 99 Posts
Originally Posted by Revracer View Post
I am currently using a 25.8 seatpost that was squeaking. I applied grease went for a 60 mile ride and found it slipped down almost 2cm. To be fair, the seatpost clamp when tight has no gap. I never had slippage when I had it in dry. I have read about the inconsistency of vintage French bikes regarding seatposts, but curious if any of you have personally fixed this by:

Find a 26.0 seatpost?
How much bigger of a seatpost is likely to fit?
Get a bigger seatpost and lightly sand until it is just right?
Carbon paste?
Anti-seize?
What model/year frame?

Google is your friend.
jiangshi is offline  
Old 04-25-20, 04:06 PM
  #4  
Revracer
Senior Member
Thread Starter
 
Revracer's Avatar
 
Join Date: Dec 2011
Location: Eastern PA, USA
Posts: 182

Bikes: 1973 Schwinn World Voyageur | Francesco Moser SL | 1984 Ross Utopian | St. Etienne 531 | 1981 Peugeot PK10 | 2015 Cannondale SuperSix | 2012 Felt F65X

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 46 Post(s)
Liked 29 Times in 13 Posts
It is actually for the St. Etienne that I suspect is a straight gauge French 531. I am curious if there is a preferred gap in the seatpost pinch.
Revracer is offline  
Old 04-25-20, 04:11 PM
  #5  
T-Mar
Senior Member
 
Join Date: Nov 2004
Posts: 20,878
Mentioned: 562 Post(s)
Tagged: 1 Thread(s)
Quoted: 3763 Post(s)
Likes: 0
Liked 1,179 Times in 876 Posts
Originally Posted by Revracer View Post
It is actually for the St. Etienne that I suspect is a straight gauge French 531. I am curious if there is a preferred gap in the seatpost pinch.
For an ideally sized post, the gap at the top of the cinch slot should only be ~0.6mm narrower than the width of the cinch slot at the bottom.
T-Mar is offline  
Old 04-25-20, 05:27 PM
  #6  
bertinjim 
Senior Member
 
bertinjim's Avatar
 
Join Date: Mar 2012
Location: Niagara Region, Canada
Posts: 1,274

Bikes: 1960s Bertin C37, 1973 Carre Bertin C 37, 1970s Carlton Kermesse, 1982 Peugeot PB 12

Mentioned: 40 Post(s)
Tagged: 0 Thread(s)
Quoted: 270 Post(s)
Liked 100 Times in 70 Posts
Revracer -

The 25.8 mm seatposts were what came on PG Carbolite hi-tensile frames on Peugeots like the PB 12 Course. Usually PG 531 was about 26.8 ish. The seatpost definitely seems under sized.
bertinjim is offline  
Old 04-25-20, 06:19 PM
  #7  
SurferRosa
Señor Member
 
SurferRosa's Avatar
 
Join Date: Dec 2018
Location: Pac NW
Posts: 3,991

Bikes: Old school lightweights

Mentioned: 55 Post(s)
Tagged: 0 Thread(s)
Quoted: 1634 Post(s)
Liked 1,662 Times in 942 Posts
Originally Posted by Revracer View Post
the seatpost clamp when tight has no gap... Find a 26.0 seatpost? ... Get a bigger seatpost and lightly sand until it is just right?
Post a pic of the collar/lug. Can you file a quick solution? Sanding down a larger seatpost is a lot easier when the bike is a keeper. You know exactly how much of the post to file for your riding position. Pretty easy.
SurferRosa is offline  
Old 04-25-20, 08:00 PM
  #8  
3alarmer
Friendship is Magic
 
3alarmer's Avatar
 
Join Date: Nov 2010
Location: The Big Tomato
Posts: 19,386

Bikes: old ones

Mentioned: 274 Post(s)
Tagged: 0 Thread(s)
Quoted: 20593 Post(s)
Liked 3,646 Times in 2,674 Posts
Originally Posted by Revracer View Post
Get a bigger seatpost and lightly sand until it is just right?
...this is what I do, mostly. Make sure you expand the top where the slot has been squeezed down before you fit the new post.
I try for a fit where there's some resistance when I slide the post in and down into the un-slotted portion of the seat tube.

Also, file off any burrs on the interior at the top, because those can confuse you on fit.
3alarmer is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.