Go Back  Bike Forums > Bike Forums > General Cycling Discussion
Reload this Page >

Seatpost Minimum Insertion

Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Seatpost Minimum Insertion

Old 07-16-20, 03:09 AM
  #1  
alij2018
Senior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 58
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 30 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Seatpost Minimum Insertion



When seatpost manufacturers specify a minimum insertion line on their seatposts, is it at point A or B on the frame?
alij2018 is offline  
Old 07-16-20, 04:09 AM
  #2  
masi61
Senior Member
 
masi61's Avatar
 
Join Date: Oct 2005
Location: SW Ohio
Posts: 2,886

Bikes: Puch Marco Polo, Saint Tropez, Masi Gran Criterium

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 728 Post(s)
Liked 152 Times in 117 Posts
Originally Posted by alij2018 View Post


When seatpost manufacturers specify a minimum insertion line on their seatposts, is it at point A or B on the frame?
I would say point A is OK so long as the bottom of the post extends to below the bottom of the top tube junction.
masi61 is offline  
Old 07-16-20, 04:15 AM
  #3  
Miele Man
Senior Member
 
Join Date: Jun 2014
Location: Ontario, Canada
Posts: 4,290

Bikes: iele Latina, Miele Suprema, Miele Uno LS, Miele Miele Beta, MMTB, Bianchi Model Unknown, Fiori Venezia, Fiori Napoli, VeloSport Adamas AX

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1166 Post(s)
Liked 732 Times in 509 Posts
I'd have my minimum insertion mark inserted at least as far as the weld below 'B'. Cantilever force can snap off the protruding seattube if there's too much seat post above that weld and not enough below it. I've seen frames ruined because that section between what you have marked 'A' and 'B' broke off because there wasn't enough seatpost below it.

Cheers
Miele Man is offline  
Likes For Miele Man:
Old 07-16-20, 05:53 AM
  #4  
dedhed
SE Wis
 
dedhed's Avatar
 
Join Date: Apr 2005
Location: Milwaukee, WI
Posts: 7,667

Bikes: '68 Raleigh Sprite, '02 Raleigh C500, '84 Raleigh Gran Prix, '91 Trek 400, 2013 Novara Randonee, 1990 Trek 970

Mentioned: 28 Post(s)
Tagged: 0 Thread(s)
Quoted: 1606 Post(s)
Liked 1,204 Times in 794 Posts
If I wasn't at least half way through the top tube I'd be looking at a longer post.
More if I were big & strong
dedhed is offline  
Old 07-16-20, 08:34 AM
  #5  
fietsbob
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,599

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,315 Times in 826 Posts
answer is C , bottom of the seat post at least in as far as the bottom of where the top tube joins the seat tube..

On my touring bike build I had a classic Campagnolo seatpost I wanted to use, since it was close to max ( because of sloping top tube)
I had a welder add a length of a common Kalloy seat post, that diameter, then get the weld bead machined down smooth..
fietsbob is offline  
Likes For fietsbob:
Old 07-16-20, 11:24 AM
  #6  
veganbikes
Clark W. Griswold
 
Join Date: Mar 2014
Location: ,location, location
Posts: 8,373

Bikes: Foundry Chilkoot Ti W/Ultegra Di2, Salsa Timberjack Ti, Cinelli Mash Work RandoCross Fun Time Machine, 1x9 XT Parts Hybrid, Co-Motion Cascadia, Specialized Langster, Phil Wood Apple VeloXS Frame (w/DA 7400), Cilo Road Frame, Proteus frame, Ti 26 MTB

Mentioned: 38 Post(s)
Tagged: 0 Thread(s)
Quoted: 2279 Post(s)
Liked 1,228 Times in 844 Posts
Originally Posted by fietsbob View Post
answer is C , bottom of the seat post at least in as far as the bottom of where the top tube joins the seat tube..

On my touring bike build I had a classic Campagnolo seatpost I wanted to use, since it was close to max ( because of sloping top tube)
I had a welder add a length of a common Kalloy seat post, that diameter, then get the weld bead machined down smooth..
I really want to see that. That seems like extreme measures but awesome and well worth it.



If you are a larger rider than get the seatpost in farther and get something of length.
veganbikes is offline  
Old 07-16-20, 11:45 AM
  #7  
fietsbob
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,599

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,315 Times in 826 Posts
The Machinist was my father (1920-2000) and his friend had a welding shop.
fietsbob is offline  
Old 07-16-20, 01:28 PM
  #8  
alij2018
Senior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 58
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 30 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Ok, mine is 3 millimeters below point B. Which is safe totally. Thanks everyone. Thread closed.
alij2018 is offline  
Old 07-16-20, 03:26 PM
  #9  
fietsbob
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,599

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,315 Times in 826 Posts
Good luck with your Assumption ..
fietsbob is offline  
Old 07-16-20, 03:53 PM
  #10  
GAtkins
Senior Member
 
Join Date: Aug 2002
Location: Springdale, Arkansas
Posts: 247

Bikes: 2021 Trek Domane SLR7 Project One 62cm- 2010 Specialized Allez 61cm

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 93 Post(s)
Liked 71 Times in 38 Posts
Originally Posted by alij2018 View Post
Ok, mine is 3 millimeters below point B. Which is safe totally. Thanks everyone. Thread closed.
That doesn't square with post #5 above.

Glenn
GAtkins is offline  
Old 07-16-20, 04:26 PM
  #11  
63rickert
Senior Member
 
Join Date: Dec 2013
Posts: 1,793
Mentioned: 43 Post(s)
Tagged: 0 Thread(s)
Quoted: 903 Post(s)
Liked 229 Times in 172 Posts
When buying used bikes first thing to look at after evidence of front end damage is condition of seat lug. Or on a frame like one in top post, top of seat tube. They are very very frequently damaged from inadequate insertion. Back when all frames were sorta similar the rule was 6 to 7 cm inside the frame. Make that 2-1/2” to 3” if you can’t speak metric. Modern frames with sloping top tubes will have huge amounts of seatpost showing. Means you need more post inside frame. Frames break and bend at this point all the time. There is not ever any reason to skimp on seatpost insertion.

On old steel frames it was possible to do lots of bending and repair that damaged seat lug. Sometimes it would be worth it to get out the torch and some brass. Modern frames mostly they get scrapped. Anyone thinking about how little insertion they can get away with will soon be scrapping a frame. Plus medical bills.
63rickert is offline  
Likes For 63rickert:
Old 07-16-20, 04:39 PM
  #12  
fietsbob
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,599

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,315 Times in 826 Posts
To be clear; the minimum insertion line on the seat post is to be at the B height ,
so the rest of the seatpost below that line is below that point?

How long is the length of that post below that minimum line ?

and as I offered above, it should be the spanning the miter width of the top tube .....
fietsbob is offline  
Old 07-16-20, 04:39 PM
  #13  
cyclist2000
Senior Member
 
cyclist2000's Avatar
 
Join Date: Sep 2009
Location: Up
Posts: 4,416

Bikes: Masi, Giant TCR, Eisentraut (retired), Jamis Aurora Elite, Zullo, Cannondale, 84 Stumpjumper, Waterford, Tern D8, Bianchi, Gunner Roadie, Serotta, and looking for a Brompton M6R

Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 256 Post(s)
Liked 1,419 Times in 408 Posts
Originally Posted by GAtkins View Post
That doesn't square with post #5 above.

Glenn
unless the op means that the minimum insertion mark is 3 mm below point b
cyclist2000 is offline  
Old 07-16-20, 04:59 PM
  #14  
tkamd73 
Senior Member
 
Join Date: Dec 2015
Location: Menomonee Falls, WI
Posts: 1,064

Bikes: 1984 Schwinn Supersport, 1988 Trek 400t, 1977 Trek TX900, 1983 Bianchi Champione del Mondo, 1986 Trek 400 Elance, 1978 Raleigh Supercourse, 1991 PDG Paramount OS, 1971 Schwinn Sports Tourer, 1985 Trek 670

Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 351 Post(s)
Liked 325 Times in 197 Posts
This is in chapter 10 of my Park Tool School instructor manual.
Tim


tkamd73 is offline  
Likes For tkamd73:
Old 07-17-20, 12:41 AM
  #15  
alij2018
Senior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 58
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 30 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Originally Posted by tkamd73 View Post
This is in chapter 10 of my Park Tool School instructor manual.
Tim


In this case, it's point A. But mine is 3mm below point B. So, I think I'm good. My seatpost is 400m length.
alij2018 is offline  
Old 07-17-20, 12:42 AM
  #16  
alij2018
Senior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 58
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 30 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Originally Posted by cyclist2000 View Post
unless the op means that the minimum insertion mark is 3 mm below point b
Correct, 3mm below point B. Seatpost is 400mm length.
alij2018 is offline  
Old 07-17-20, 02:35 AM
  #17  
onyerleft
Senior Member
 
onyerleft's Avatar
 
Join Date: Jan 2018
Posts: 485

Bikes: Pedaling for the Lord!

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 313 Post(s)
Likes: 0
Liked 54 Times in 36 Posts
I treat minimum seatpost markings like my crack: I never want either one to show. But if I were an electrician, handyman, HVAC repairman or plumber, I might not care so much about the latter....
onyerleft is offline  
Old 07-17-20, 06:12 AM
  #18  
SJX426 
Senior Member
 
SJX426's Avatar
 
Join Date: May 2008
Location: Fredericksburg, Va
Posts: 7,843

Bikes: '73 Bottecchia Giro d'Italia, '83 Colnago Superissimo, '84 Trek 610, '84 Trek 760, '88 Pinarello Veneto, '88 De Rosa Pro, '90 De Rosa Professional, '91 Pinarello Montello, '94 Burley Duet, 97 Specialized RockHopper, 2010 Langster, Tern Link D8

Mentioned: 56 Post(s)
Tagged: 0 Thread(s)
Quoted: 1018 Post(s)
Liked 671 Times in 418 Posts
I measured two Campagnolo posts. Both, a Chorus Aero and a NR, measured 57mm (2.25:") from the top of the line to the end of the post. I believe that may be enough to get the end to the bottom of the seat lug. Your risk.
__________________
Bikes don't stand alone. They are two tired.
SJX426 is offline  
Old 07-17-20, 09:57 AM
  #19  
tkamd73 
Senior Member
 
Join Date: Dec 2015
Location: Menomonee Falls, WI
Posts: 1,064

Bikes: 1984 Schwinn Supersport, 1988 Trek 400t, 1977 Trek TX900, 1983 Bianchi Champione del Mondo, 1986 Trek 400 Elance, 1978 Raleigh Supercourse, 1991 PDG Paramount OS, 1971 Schwinn Sports Tourer, 1985 Trek 670

Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 351 Post(s)
Liked 325 Times in 197 Posts
Originally Posted by alij2018 View Post
In this case, it's point A. But mine is 3mm below point B. So, I think I'm good. My seatpost is 400m length.
Agreed!
Tim
tkamd73 is offline  
Old 07-17-20, 11:40 AM
  #20  
Miele Man
Senior Member
 
Join Date: Jun 2014
Location: Ontario, Canada
Posts: 4,290

Bikes: iele Latina, Miele Suprema, Miele Uno LS, Miele Miele Beta, MMTB, Bianchi Model Unknown, Fiori Venezia, Fiori Napoli, VeloSport Adamas AX

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1166 Post(s)
Liked 732 Times in 509 Posts
Any seatpost that was inserted only to Point B would have a lot of leverage/torque on that part of the seattube that's above the toptube of the bike. The more seatpost above the toptube and the heavier the rider the more leverage/torque there is. Its a failure waiting to happen. I tell people to make sure that at least TWO INCHES of their seatpost is BELOW the top of their toptube. I'm glad you did that. Having a seattube break off on a long ride is unpleasane at bast dangerous to the rider, and often the ruination of the frame.

Cheers
Miele Man 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.