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

Seat post questions...

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.

Seat post questions...

Old 06-30-22, 10:23 AM
  #1  
ArgoMan
Junior Member
Thread Starter
 
Join Date: Jun 2022
Posts: 196
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 147 Post(s)
Likes: 0
Liked 24 Times in 21 Posts
Seat post questions...

Good morning everyone!

Continuing with my build questions , I have an early 90's "Geoid" Scapin frame that I'm building out. Using my Swiss made vernier calipers, I get an interior tube reading of 26.6. So I then go onto the various websites looking for an appropriate seat post, which to my dismay is a confusing topic. So many post dimensions! Several manufacturers make a 26.6mm post. Some make a 26.5 and 26.4mm post. I'm assuming that I need a 26.6mm post, but I saw some commentary that I may wish to go with a slightly smaller diameter. To that issue, what to you all say?

Next, 26.6mm seems to be a rather obscure diameter. But I found some cheaper-priced posts that seem to fit the bill (aluminum) by a company named "Kalloy." But they are single bolt posts. I don't know what that means for fit and performance. I also found a guy on eBay selling Kalloy posts that are "micro adjustable". Sound interesting. I also found a number of sellers on eBay selling used or NOS posts that have a "double bolt attachment" (I think that's the phrase), made in either Japan or Italy, which I like the idea of. I am weary of a Chinese manufactured aluminum post that may fracture, as I've read some stories online of this happening and am familiar with Chinese manufacturing practice compared with others, like Japanese or Taiwanese. Any thoughts and suggestions would be very welcome. I'd especially appreciate Smelly's input, as he is really a store of great knowledge.
ArgoMan is offline  
Old 06-30-22, 10:35 AM
  #2  
seypat
Senior Member
 
Join Date: Oct 2010
Posts: 8,758
Mentioned: 69 Post(s)
Tagged: 0 Thread(s)
Quoted: 3192 Post(s)
Liked 2,461 Times in 1,490 Posts
Hit the red button under your post and have the thread moved to C & V. You'll get a lot more interest/answers there.
seypat is offline  
Old 06-30-22, 10:38 AM
  #3  
Iride01 
I'm good to go!
 
Iride01's Avatar
 
Join Date: Jul 2017
Location: Mississippi
Posts: 14,811

Bikes: Tarmac Disc Comp Di2 - 2020

Mentioned: 50 Post(s)
Tagged: 0 Thread(s)
Quoted: 6100 Post(s)
Liked 4,732 Times in 3,262 Posts
Depends on a lot more stuff than what you measured with your Swiss made Vernier calipers. Actually they aren't the precise way to measure the inside diameter of any round tube needing real accuracy. Nor do they get deep enough into the tube to be where you can get a measurement that hasn't been affected by the years of clamping and unclamping the seat post clamp.

You do want the post to be smaller in diameter than the part of the tube below the clamp. Since your seat tube probably has a slit cut in it, it will be okay if the size of it actually measures the same or even smaller than your seat post as that part of the tube will open more when you insert the seat post.

So it's really a try it and see sort of thing. Possibly you might need to ream the tube if it's been mucked up by years of abuse.
Iride01 is offline  
Old 06-30-22, 10:50 AM
  #4  
ArgoMan
Junior Member
Thread Starter
 
Join Date: Jun 2022
Posts: 196
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 147 Post(s)
Likes: 0
Liked 24 Times in 21 Posts
Originally Posted by Iride01
Depends on a lot more stuff than what you measured with your Swiss made Vernier calipers. Actually they aren't the precise way to measure the inside diameter of any round tube needing real accuracy. Nor do they get deep enough into the tube to be where you can get a measurement that hasn't been affected by the years of clamping and unclamping the seat post clamp.

You do want the post to be smaller in diameter than the part of the tube below the clamp. Since your seat tube probably has a slit cut in it, it will be okay if the size of it actually measures the same or even smaller than your seat post as that part of the tube will open more when you insert the seat post.

So it's really a try it and see sort of thing. Possibly you might need to ream the tube if it's been mucked up by years of abuse.
Yes, thank you! I don't recall right now if the post as a slit. I can ream it easily enough and will have to polish the inside a bit, as there's some "muck" therein. I can also "shim" a post is needed. What are your thoughts of a single or double post, and the micro adjustable posts?

Thanks again!
ArgoMan is offline  
Old 06-30-22, 11:57 AM
  #5  
Iride01 
I'm good to go!
 
Iride01's Avatar
 
Join Date: Jul 2017
Location: Mississippi
Posts: 14,811

Bikes: Tarmac Disc Comp Di2 - 2020

Mentioned: 50 Post(s)
Tagged: 0 Thread(s)
Quoted: 6100 Post(s)
Liked 4,732 Times in 3,262 Posts
Originally Posted by ArgoMan
Yes, thank you! I don't recall right now if the post as a slit. I can ream it easily enough and will have to polish the inside a bit, as there's some "muck" therein. I can also "shim" a post is needed. What are your thoughts of a single or double post, and the micro adjustable posts?

Thanks again!
Though I mentioned reaming, I wouldn't ream the tube unless the inside surface is so bad that it makes inserting the seat post smoothly difficult. As to double or single I guess you are talking about the clamp for the saddle.

I like the two bolt clamps that let me have infinite adjustment of the tilt of the saddle. Some people find they are more difficult to use. You'll have to make your own personal assessment of what you prefer. But there are newer seat posts with a single bolt that work entirely different than those of the era your bike is from. My newest bike has a single bolt saddle clamp on the seat post and it works very well. Don't have any reason to change it to the two bolt that I've long preferred.
Iride01 is offline  
Old 06-30-22, 12:21 PM
  #6  
t2p
Senior Member
 
Join Date: May 2022
Location: USA - Southwest PA
Posts: 2,981

Bikes: Cannondale - Gary Fisher - Giant - Litespeed - Schwinn Paramount - Schwinn (lugged steel) - Trek OCLV

Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1359 Post(s)
Liked 1,803 Times in 1,038 Posts
Thomson makes a quality seatpost - including 26.6

mighy be able to find an old Suntour Superbe 26.6 seatpost ?

Ritchey ... Kalloy ... American Classic ? ...

Origin 8 ? ...
t2p is offline  
Old 06-30-22, 12:29 PM
  #7  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,845

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1173 Post(s)
Liked 924 Times in 610 Posts
Moved from Road forum.
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: https://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 06-30-22, 12:43 PM
  #8  
Andy_K 
Senior Member
 
Andy_K's Avatar
 
Join Date: Jan 2008
Location: Beaverton, OR
Posts: 14,787

Bikes: Yes

Mentioned: 522 Post(s)
Tagged: 0 Thread(s)
Quoted: 3228 Post(s)
Liked 3,854 Times in 1,436 Posts
There are two ways to determine seatpost size. One is to try seatposts of various sizes and see which one fits. The other is to use a specialized stepped tool which does effectively the same thing. Since you probably don't have various sized seatposts or the tool, your best bet is to take the frame to a shop which can do this for you.

Using the wrong size seatpost will cause problems. I wouldn't recommend guessing.
__________________
My Bikes
Andy_K is offline  
Old 06-30-22, 12:59 PM
  #9  
Wildwood 
Veteran, Pacifist
 
Wildwood's Avatar
 
Join Date: Dec 2004
Location: Seattle area
Posts: 13,305

Bikes: Bikes??? Thought this was social media?!?

Mentioned: 284 Post(s)
Tagged: 0 Thread(s)
Quoted: 3876 Post(s)
Liked 4,781 Times in 2,206 Posts
26.6mm is the post diameter on my '72 Zeus with metric 531 tubing; 26.4 pinches the lug's ears too much.
Make a post in the 'for trade' thread and get a vintage post for your vintage bike. It will not have been made in China, if that is a concern of yours.

Anyone who suggests getting any seatpost diameter but the correct one for your frame - should not be taken seriously.
__________________
Vintage, modern, e-road. It is a big cycling universe.

Last edited by Wildwood; 06-30-22 at 01:02 PM.
Wildwood is offline  
Old 06-30-22, 01:15 PM
  #10  
randyjawa 
Senior Member
 
randyjawa's Avatar
 
Join Date: Apr 2007
Location: Thunder Bay, Ontario, Canada - burrrrr!
Posts: 11,672

Bikes: 1958 Rabeneick 120D, 1968 Legnano Gran Premio, 196? Torpado Professional, 2000 Marinoni Piuma

Mentioned: 210 Post(s)
Tagged: 0 Thread(s)
Quoted: 1370 Post(s)
Likes: 0
Liked 1,743 Times in 934 Posts
When measuring a seat post cavity, I measure in five locations, add the fire measurements up and divide by five. This method helps to account for any ovality that might have occurred during years of use. When installing a seat post, I install one that is tight, not loose at all. A slightly loose post will usually alloy the clamp assembly to distort and, more often than not, the post will slip.

Before measuring, I use emery cloth to clean the inside of the seat post cavity. Up and down, round and round, and repeat as often as necessary to get things clean. If there is any ovality, I try to eliminate it as best I can. Usually, the distortion is around the clamp ears. Finally, I use a small smooth round file to clean up the slot in the seat tube. I try to slightly camphor the edges of the slot, reducing the chances of scoring the alloy seat post. With all that done, I find the tightest seat post and install it. A proper sized seat post done not have to be super duper snugged up. Super duper snugging will, often times, just bend the seat clamp bolt and/or distort the clamp ears

It all might sound like a lot of work, but a half hour's effort will, usually, do the trick. When ever attempting to fit the post, always ensure that it is greased, even for trial fits. Best of luck.
__________________
"98% of the bikes I buy are projects".
randyjawa is offline  
Likes For randyjawa:
Old 06-30-22, 01:19 PM
  #11  
unworthy1
Stop reading my posts!
 
unworthy1's Avatar
 
Join Date: Sep 2004
Posts: 12,959
Mentioned: 89 Post(s)
Tagged: 0 Thread(s)
Quoted: 1422 Post(s)
Liked 1,038 Times in 769 Posts
Kalloy makes several "nothing fancy but perfectly fine" seat posts. I have used them on many builds, a big plus is the big range of size these are available in, I consider them a good value, if not great lookers.
But you can get into trouble with a caliper (yes, even a Swiss digital model) when trying to get accurate internal seat tube dims. You're better off taking it to a LBS that has a post sizer "mandrel" they can use, maybe even a few donor posts they can try out for the final word on fit.
But do you know exactly what tubing this Scapin is built with, esp. that seat tube?
I never heard of this Geoid model, but Scapin used a lot of the lower priced Columbus tubes (as well as the highest grades) like Gara, Zeta, etc. to cover all the price points

Last edited by unworthy1; 06-30-22 at 01:22 PM.
unworthy1 is offline  
Likes For unworthy1:
Old 06-30-22, 01:50 PM
  #12  
Chombi1 
Senior Member
 
Chombi1's Avatar
 
Join Date: Nov 2015
Posts: 4,457
Mentioned: 102 Post(s)
Tagged: 0 Thread(s)
Quoted: 1629 Post(s)
Likes: 0
Liked 814 Times in 527 Posts
I too was not familiar with 26.6 mm diameter post either till I started building up my 1983 Gitane Pro.
Was surprised to find out the Simplex SLJ seatpost on it was a 26.6 diameter as I thought most French bikes with metric tubing uses 26.4 diameter posts.
__________________
72 Line Seeker
83 Davidson Signature
84 Peugeot PSV
84 Peugeot PY10FC
84 Gitane Tour de France.
85 Vitus Plus Carbone 7
86 ALAN Record Carbonio
86 Medici Aerodynamic (Project)
88 Pinarello Montello
89 Bottecchia Professional Chorus SL
95 Trek 5500 OCLV (Project)
Chombi1 is offline  
Old 06-30-22, 01:52 PM
  #13  
repechage
Senior Member
 
Join Date: Jun 2006
Posts: 20,323
Mentioned: 129 Post(s)
Tagged: 0 Thread(s)
Quoted: 3449 Post(s)
Liked 2,800 Times in 1,974 Posts
Vernier calipers are not designed well for the task of measuring a seat tube.

a telescoping bore gauge would be the reasonable cost way to go.

I would want to measure 3-4 cm below the opening, beyond the heat effected zone is the point.

then a number of other radial measures at a few stations. My hunch you will find variance and smaller at the top.

review why that might be so, if an undersized post had been inserted prior, easily closed up.

an example - a 1972 49cm Colnago super I bought had a 27.0 post. Even after truing up the slot region a 27.2 would not go.
the tube was 27.2 below the lug. Time for the reamer. Now 27.2 happy.
should have been done at the original assembly- all paint in the tube was there still.

the odds of such a small frame being built with SP tubes? Very low.

there are nice high quality digital bore gauges...
$$$, but really nice and quick to get the real answer. They use three points to assess the diameter.
repechage is offline  
Old 06-30-22, 02:00 PM
  #14  
gugie 
Bike Butcher of Portland
 
gugie's Avatar
 
Join Date: Jul 2014
Location: Portland, OR
Posts: 11,641

Bikes: It's complicated.

Mentioned: 1299 Post(s)
Tagged: 0 Thread(s)
Quoted: 4670 Post(s)
Liked 5,769 Times in 2,272 Posts
You can come on by and check with my gauge.



Post your location. There's a reasonable chance you're nearby a BF member with the tool you need.
__________________
If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.
gugie is offline  
Old 06-30-22, 02:09 PM
  #15  
aliasfox
Senior Member
 
Join Date: Aug 2019
Location: SF Bay Area
Posts: 625

Bikes: Lynskey R270 Disc, Bianchi Vigorelli

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 298 Post(s)
Liked 154 Times in 129 Posts
+1 on the Thomson - it is so choice. If you have the means, I highly recommend picking one up.

I got a Thomson Elite to replace the single bolt seatpost on my hardtail 20 years ago. It's now the post that I use on my Bianchi. I have a Masterpiece on my Lynskey, as well.

The problems with a single-bolt post are that it relies on serrations in the clamp to dictate saddle angle, so you're unable to make very-fine tweaks. Additionally, if your weight is resting on the rear of the saddle, behind the bolt, it acts as a lever - making that bolt a single point of failure, which is what happened with my single-bolt post on my hardtail.
aliasfox is offline  
Old 06-30-22, 02:11 PM
  #16  
wrk101
Thrifty Bill
 
wrk101's Avatar
 
Join Date: Jan 2008
Location: Mountains of Western NC
Posts: 23,572

Bikes: 86 Katakura Silk, 87 Prologue X2, 88 Cimarron LE, 1975 Sekai 4000 Professional, 73 Paramount, plus more

Mentioned: 96 Post(s)
Tagged: 0 Thread(s)
Quoted: 1236 Post(s)
Liked 957 Times in 624 Posts
People tend to bash China made product on every forum. Often they do it on their Apple computer or Apple phone that is made in China..... Go figure....

Anyway, in my own manufacturing experience, China makes some outstanding stuff, some mediocre stuff, and everything in between. Its more about what the customer wants, rather than China making crappy stuff.

BTW, in the world of cheap manufacturing, China is no longer "cheap". Check out various well known branded bikes that are now made in Cambodia.

On seat posts, I keep a box full. Some 26.6 posts will measure close to 26.6, others will be closer to 26.4, even though they are marked 26.6.

The Stein tool above is a good one.

I tend to run a brake hone into the seat tube, particularly if the existing seat post has zigzag marks on it. I don't get carried away with the home, its just knocking down any high spots inside the tube.
wrk101 is offline  
Old 06-30-22, 04:21 PM
  #17  
unworthy1
Stop reading my posts!
 
unworthy1's Avatar
 
Join Date: Sep 2004
Posts: 12,959
Mentioned: 89 Post(s)
Tagged: 0 Thread(s)
Quoted: 1422 Post(s)
Liked 1,038 Times in 769 Posts
pretty sure Scapin would not have built with any type metric tubing, Columbus or other.
But yeah, the metric "good stuff" DB tubing could take either 26.4 or 26.6, depending on how it was reamed.
unworthy1 is offline  
Old 06-30-22, 04:38 PM
  #18  
merziac
Senior Member
 
merziac's Avatar
 
Join Date: Oct 2015
Location: PDX
Posts: 14,101

Bikes: Merz x 5 + Specialized Merz Allez x 2, Strawberry/Newlands/DiNucci/Ti x3, Gordon, Fuso/Moulton x2, Bornstein, Paisley,1958-74 Paramounts x3, 3rensho, 74 Moto TC, 73-78 Raleigh Pro's x5, Marinoni x2, 1960 Cinelli SC, 1980 Bianchi SC, PX-10 X 2

Mentioned: 267 Post(s)
Tagged: 0 Thread(s)
Quoted: 4494 Post(s)
Liked 6,300 Times in 3,633 Posts
Originally Posted by randyjawa
When measuring a seat post cavity, I measure in five locations, add the fire measurements up and divide by five. This method helps to account for any ovality that might have occurred during years of use. When installing a seat post, I install one that is tight, not loose at all. A slightly loose post will usually alloy the clamp assembly to distort and, more often than not, the post will slip.

Before measuring, I use emery cloth to clean the inside of the seat post cavity. Up and down, round and round, and repeat as often as necessary to get things clean. If there is any ovality, I try to eliminate it as best I can. Usually, the distortion is around the clamp ears. Finally, I use a small smooth round file to clean up the slot in the seat tube. I try to slightly camphor the edges of the slot, reducing the chances of scoring the alloy seat post. With all that done, I find the tightest seat post and install it. A proper sized seat post done not have to be super duper snugged up. Super duper snugging will, often times, just bend the seat clamp bolt and/or distort the clamp ears

It all might sound like a lot of work, but a half hour's effort will, usually, do the trick. When ever attempting to fit the post, always ensure that it is greased, even for trial fits. Best of luck.
Especially for all trial fitting IMO, and all others too.
merziac is offline  
Old 06-30-22, 06:11 PM
  #19  
bikingshearer 
Crawlin' up, flyin' down
 
bikingshearer's Avatar
 
Join Date: Jan 2006
Location: Democratic Peoples' Republic of Berkeley
Posts: 5,625

Bikes: 1967 Paramount; 1982-ish Ron Cooper; 1978 Eisentraut "A"; two mid-1960s Cinelli Speciale Corsas; and others in various stages of non-rideability.

Mentioned: 40 Post(s)
Tagged: 0 Thread(s)
Quoted: 1008 Post(s)
Liked 2,465 Times in 1,030 Posts
As to the 2-bolt vs 1-bolt question: I prefer 2-bolt posts because the tilt of the saddle on them is truly infinitely adjustable. The ones with the two bolts on top (Campagnolo and its imitators) are something of a PITA to adjust, but a 10mm ratcheting box-end wrench in through the back of the saddle between the rails gets it done without too much fuss or bother. If you look hard enough (eBay is your friend here), you can find Campy 2-bolt posts in pretty much any conceivable size - 26.4mm and 26.6mm very much included.

Having said that, if you need a 26.8mm or 27.2mm post, you can't do better than a Nitto S83 (two allen bolts on the bottom, easier to work with) but they ain't cheap (about $125 from Rivendell).

My issue with single-bolt designs is they all rely on serrations to keep everything in place, tilt-wise, and I usually find I want the adjustment to end up exactly between two of the serrations. It isn't the end of the world, and I am currently successfully using one or two 1-bolt posts, but I mostly have 2-bolt posts and, as I said, I prefer them.

Full disclosure: When I started getting serious about cycling as a teenager in the 1970s, a two-bolt Campy seat post was one immediate indicator of a good bike worthy of closer examination. Because of that, I wanted one and I grew to love the look of them. I still do. The fact that they work great is why I still use them when possible, but the scratch of my nostalgia itch is icing on the cake.
__________________
"I'm in shape -- round is a shape." Andy Rooney
bikingshearer is offline  
Likes For bikingshearer:
Old 07-01-22, 07:18 AM
  #20  
T-Mar
Senior Member
 
Join Date: Nov 2004
Posts: 23,233
Mentioned: 652 Post(s)
Tagged: 1 Thread(s)
Quoted: 4719 Post(s)
Likes: 0
Liked 3,034 Times in 1,874 Posts
Geoid was simply Scapin's terminology for Columbus' teardrop shaped Megatube concept. Megatube was introduced for the 1995 model year and was a Bianchi exclusive for that year. Consequently, a Scapin with Geoid tubing is no earlier than 1996.

As for the post diameter, I can't imagine it being anything other than 27.2mm. The vast majority of the standard outside diameter (28.6mm), steel, seat tubes offered by Columbus in the late 1990s used a 27.2mm post. The only exceptions of which I'm aware were Utrafoco, which used a 27.4mm post, and Aelle and Gara, both of which used a 26.8mm post. I certainly wouldn't expect Aelle or Gara to be used on a high end Scapin. Besides, they weren't offered with a Megatube option.

That still leaves several possibilities:

1, Caliper cleanliness and calibration: Clean the jaws and slide of the caliper and make sure it zeroes properly with the jaws closed. Examine the jaws for nicks.

2. Build-up on the inside of the tube: Check for burrs around the top edge of the tube, cinch slot cut and vent hole. Remove as necessary. Remove any foreign material on the inside of the tube.

3, Distorted seat tube: Distorted seat tubes can result from the manufacturing process or an undersize post being installed. Distortion created during manufacturing typically results in varying measurements when taken across different angles. Also, take several measurements of the outside diameter of the post just below the top tube to see if the tube is still distorted at that point. If so, the inside of the tube will have to be reamed.

If the outside of the tube is round when measured just below the top tube, the issue likely results from an undersize post or at least can be treated like an undersize post issue. Undersize posts typically result in a cinch slot with non-parallel sides. For this amount of variation, the cinch slot would be visibly narrower at the top of the slot, than at the bottom. If so, gently pry the slot open with a wide, flat bladed screwdriver of similar tool, so that the cinch slot is slightly wider at the top than the bottom. This will open up the top of the seat tube, allowing you to test post fit posts past the bottom of the cinch slot, where the tube should be not be distorted.

Last edited by T-Mar; 07-01-22 at 07:23 AM.
T-Mar is offline  
Old 07-01-22, 07:27 AM
  #21  
smd4
Senior Member
 
Join Date: Dec 2020
Location: Wake Forest, NC
Posts: 5,642

Bikes: 1989 Cinelli Supercorsa

Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 3431 Post(s)
Liked 2,826 Times in 1,723 Posts
Originally Posted by aliasfox
+1 on the Thomson - it is so choice. If you have the means, I highly recommend picking one up.
+1 for the FB reference.
smd4 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 -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.