Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Reply
 
Thread Tools Search this Thread
Old 12-26-06, 02:27 PM   #1
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
seat post (railed) height extender ??

Anyone know of an "male-female" extension that basically adds a few inches of height to a standard railed seatpost?

It would have railes at the bottom, and the same railed acceptor-of-rails at the top for a normal seat.

For seatposts that are just a bit too small, and of a strange diameter, or where the max seatpost length has already been found.
jasong is offline   Reply With Quote
Old 12-26-06, 07:07 PM   #2
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Posts: 28,687
Quote:
Originally Posted by jasong
Anyone know of an "male-female" extension that basically adds a few inches of height to a standard railed seatpost?

It would have railes at the bottom, and the same railed acceptor-of-rails at the top for a normal seat.

For seatposts that are just a bit too small, and of a strange diameter, or where the max seatpost length has already been found.
I've never seen anything like this offered for sale. I expect it would be very expensive to manufacture and a new seatpost of the correct length and type would be cheaper. Seatposts are available up to 400 mm in length and shims are available to make standard diameter posts fit almost any odd-size seat tube.
HillRider is offline   Reply With Quote
Old 12-26-06, 09:35 PM   #3
operator
cab horn
 
Join Date: Jun 2004
Location: Toronto
Bikes: 1987 Bianchi Campione
Posts: 28,306
Buy a new seatpost of the correct length
operator is offline   Reply With Quote
Old 12-27-06, 03:53 AM   #4
LWaB
Senior Member
 
Join Date: Dec 2005
Location: Auld Blighty
Bikes: Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
Posts: 2,240
Sidetrak did a suspension insert that did exactly what you are looking for - never seen one in the flesh though. According to http://www.sidetrak.com/Catalog/components.html they still sell them.
LWaB is offline   Reply With Quote
Old 12-27-06, 07:11 PM   #5
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Quote:
Originally Posted by operator
Buy a new seatpost of the correct length
Op/HillR: this often times isn't possible. For instance, several folding bikes come with strange seat tubes that can't be replaced, and don't accomodate a large enough inseam for certain riders. But they are often within 50mm of being correct. Can you find a >500mm 27.2mm seatpost?

LWabs link shows that this isn't a very expensive thing to fabricate; no more technology than a seat/seatpost.

Any other solutions others have seen out there?
jasong is offline   Reply With Quote
Old 12-27-06, 07:32 PM   #6
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Posts: 28,687
Quote:
Originally Posted by jasong
Op/HillR: this often times isn't possible. For instance, several folding bikes come with strange seat tubes that can't be replaced, and don't accomodate a large enough inseam for certain riders.
Bike Fridays are sized to the owner's specs so they shouldn't have this problem unless you buy a used one and get the wrong size by a lot. If the frame is anywhere near big enough, the original manufactirer should be able to supply an adequate length post. If the longest post available isn't long enough the frame is way too small. Further, there are safety considerations with using an excessively long seat post. There aren't any 500 mm 27.2 mm seatposts for a good reason.
HillRider is offline   Reply With Quote
Old 12-28-06, 12:43 AM   #7
LWaB
Senior Member
 
Join Date: Dec 2005
Location: Auld Blighty
Bikes: Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
Posts: 2,240
Quote:
Originally Posted by HillRider
If the frame is anywhere near big enough, the original manufactirer should be able to supply an adequate length post. If the longest post available isn't long enough the frame is way too small.
Bollocks!
Have you seen how short the seatposts are on some older bikes (less than 150mm end to end)? Older French bikes in particular have unique seatpost sizes and they are simply not available nowadays. This is not an ideal solution but it is a viable one.
LWaB is offline   Reply With Quote
Old 12-28-06, 03:05 AM   #8
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Quote:
Originally Posted by HillRider
Bike Fridays are sized to the owner's specs so they shouldn't have this problem unless you buy a used one and get the wrong size by a lot. If the frame is anywhere near big enough, the original manufactirer should be able to supply an adequate length post. If the longest post available isn't long enough the frame is way too small. Further, there are safety considerations with using an excessively long seat post. There aren't any 500 mm 27.2 mm seatposts for a good reason.
HR: First, BF is one of many, many mfctrs of folders.

Downtube folders ships with a 500mm 27.2mm seatpost.

One might argue from the standpoint of a Brompton: it ships with a seatpost that isn't long enough for some, so they sell another. The frame doesn't have to be modified for the longer seatpost.

The mfctr of the seat tube will state whether or not there are safety considerations, not the mfctr of the folder. Because the same torque can be generated with a heavy person on a smaller extension vs. a light person (me) with a long extension. Remember from physics, T = r x F.

http://en.wikipedia.org/wiki/
jasong is offline   Reply With Quote
Old 12-28-06, 03:51 AM   #9
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Quote:
Originally Posted by LWaB
Bollocks!
Have you seen how short the seatposts are on some older bikes (less than 150mm end to end)? Older French bikes in particular have unique seatpost sizes and they are simply not available nowadays. This is not an ideal solution but it is a viable one.
BTW, I just picked up a Starnord randonnee bicycle in France and have needed to upgrade some of its components. It, too, shipped with a very short (6") seatpost. Which makes no sense, because the frame is ~58cm. To get to 790mm from BB center, which I doubt is all that strange for someone that needs a frame of this size, I had to find a new seatpost. It uses a 25.0 mm post, but I managed to get a 25.4 post in there.

Everything is unstandard on this bike. BB threads are spaced a little off, pedal threads are same pitch, but different height, 124mm OLD rear dropout, ...... At least none of the parts were seized. Still can't find info on this line of bikes or a good age estimate (owner said 10 years, but no way that's true).
jasong is offline   Reply With Quote
Old 12-28-06, 07:30 AM   #10
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Posts: 28,687
Quote:
Originally Posted by LWaB
Bollocks!
Have you seen how short the seatposts are on some older bikes (less than 150mm end to end)? Older French bikes in particular have unique seatpost sizes and they are simply not available nowadays. This is not an ideal solution but it is a viable one.
"Short" seatposts (Campy's used to be 180 mm) were common before the modern trend to buying the smallest possible frame you can ride came along. Racers were told to ride a small frame because it would be lighter and stiffer. The concept spilled over to the casual rider who wanted to look like a racer. To make the reach to the bars proper, manufacturers started to lengthen the top tubes on smaller frames and, of course, seatposts had to be longer.

Now a rider who would have bought a 58 cm frame in the past buys a 54 or 55 but needs a 230 or 250 mm seatpost. Of course "compact" frames with sloping toptubes, both road and MTB, require even longer seatposts and now we have 300 to 400 mm posts in common use.

jsong, your 58 cm Starnord that came with the 150 mm seatpost was intended for a rider about 5'9" (1.75 M) or a bit shorter. If you need a 790 mm (31.1") seat height, you would have bought a 60 or 61 cm frame in those days. Also, 25.0 mm seatposts are available.
HillRider is offline   Reply With Quote
Old 12-28-06, 12:13 PM   #11
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Quote:
Originally Posted by HillRider
jsong, your 58 cm Starnord that came with the 150 mm seatpost was intended for a rider about 5'9" (1.75 M) or a bit shorter. If you need a 790 mm (31.1") seat height, you would have bought a 60 or 61 cm frame in those days. Also, 25.0 mm seatposts are available.
Problem with this is that I'm already stretched to ride on the brakehoods, and it has a small (~100mm) stem. I think I have a fairly normal body type: 6', 34.5" inseam. Just shows what riding style may have been common in the past.
jasong is offline   Reply With Quote
Old 12-28-06, 04:10 PM   #12
howsteepisit
Senior Member
 
howsteepisit's Avatar
 
Join Date: Oct 2005
Location: Eugene, OR
Bikes: Mecian
Posts: 3,605
Jasong,

I am really similar in size to you, I ride a 62 - 64 cm bike. sounds like your starnord has a very longish top tube, or you have fairly short arms. Have you seen a professional fitter? BTW, can you now remove the 25.4 seatpost? I certainly hope you greased it.
howsteepisit is offline   Reply With Quote
Old 12-28-06, 08:26 PM   #13
LWaB
Senior Member
 
Join Date: Dec 2005
Location: Auld Blighty
Bikes: Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
Posts: 2,240
Quote:
Originally Posted by HillRider
Also, 25.0 mm seatposts are available.
Certainly but good luck finding a 23.8mm post, as I needed once.
LWaB is offline   Reply With Quote
Old 12-28-06, 08:53 PM   #14
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Posts: 28,687
Quote:
Originally Posted by LWaB
Certainly but good luck finding a 23.8mm post, as I needed once.
That's right and 25.0 is about the smallest used in the past 20 years or so. What needed a 23.8?
HillRider is offline   Reply With Quote
Old 12-28-06, 09:36 PM   #15
LWaB
Senior Member
 
Join Date: Dec 2005
Location: Auld Blighty
Bikes: Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
Posts: 2,240
The bike was older than 20 years. The French can be a little difficult sometimes...
LWaB is offline   Reply With Quote
Old 12-29-06, 04:31 AM   #16
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Decathlon in France sells a 350mm 23.4 post with two shims to fit between ~25 and I think 28ish. €15 for the kit.
jasong is offline   Reply With Quote
Old 12-29-06, 05:16 AM   #17
LWaB
Senior Member
 
Join Date: Dec 2005
Location: Auld Blighty
Bikes: Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
Posts: 2,240
OT: Those adjustable shims aren't too secure and weren't available when I was looking, also France isn't quite next door to me. The problem was solved a decade ago by machining another seatpost to fit but it isn't the easiest solution...
LWaB is offline   Reply With Quote
Old 12-29-06, 08:49 AM   #18
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Posts: 28,687
Quote:
Originally Posted by LWaB
The French can be a little difficult sometimes...
One of the more astute comments I've read recently.
HillRider is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

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



All times are GMT -6. The time now is 04:13 AM.