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.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 03-31-12, 03:57 PM   #1
onespeedbiker
Retro Grouch
Thread Starter
 
onespeedbiker's Avatar
 
Join Date: Oct 2007
Location: Santa Cruz
Bikes: Yes
Posts: 2,210
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
How short is long enough?

I recently bought a new seatpost (Nitto S-83); a great deal at 35% off. Unfortunately when it arrived it was a 300mm and I ordered a 250mm. I emailed the vender and they said they would pay postage for the return but they don't have any 250mm to replace it with. Due to the fact that I can just cut it down I declined. The issue now is how short. The post the new post is replacing was a 250mm, but even it was long longer than it needed. The bike has standard geometry and can use a very short seatpost, i.e. less than 180-200mm would work with plenty to spare. Is there any reason I should not cut it down to 200mm?
onespeedbiker is offline   Reply With Quote
Old 03-31-12, 04:25 PM   #2
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 29,421
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 94 Post(s)
You need roughly 60mm inside the frame, or enough to reach 25mm below the bottom of the top tube (whichever is deeper). Knowing that you can feel free to cut any extra length off, but leave yourself a margin for error, since the added weight of 10mm of post in negligible.

So set your final seat height and mark the post where it emerges from the frame. Put the post next to the seat tube and determine where the bottom needs to reach and draw your cut line anywhere below that. The only thing you're giving up is some ability to resell the bike to a taller person.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FBinNY is offline   Reply With Quote
Old 03-31-12, 04:27 PM   #3
cyclist2000
Senior Member
 
cyclist2000's Avatar
 
Join Date: Sep 2009
Location: Up
Bikes: Masi (retired), Giant TCR, Eisentraut, Jamis Aurora Elite, Zullo (trainer bike), Cannondale, 84 Stumpjumper, Waterford(N+1), Tern D8 (N+1), looking for a Ti frame
Posts: 3,025
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Why cut it at all? Leaving it full length helps resale possibilities.
cyclist2000 is offline   Reply With Quote
Old 03-31-12, 04:35 PM   #4
dsbrantjr
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta
Posts: 4,498
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 33 Post(s)
+1 for leaving it full length if you can fit it far enough into the frame. I don't see any downside to leaving it longer except for the minor weight savings.
dsbrantjr is offline   Reply With Quote
Old 03-31-12, 04:42 PM   #5
hueyhoolihan
Senior Member
 
Join Date: Dec 2010
Location: Above ground, Walnut Creek, Ca
Bikes: 7⃥ 9 road bikes
Posts: 6,401
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
i'm kind of sensitive about excess weight on my bikes, but even I might hesitate to cut just 50mm.
hueyhoolihan is offline   Reply With Quote
Old 03-31-12, 06:04 PM   #6
JiveTurkey
Low car diet
 
JiveTurkey's Avatar
 
Join Date: Aug 2007
Location: Corvallis, OR, USA
Bikes: 2006 Windsor Dover w/105, 2007 GT Avalanche w/XT, 1995 Trek 820 setup for touring, 201? Yeah single-speed folder, 199? Huffy tandem.
Posts: 2,407
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by FBinNY View Post
but leave yourself a margin for error, since the added weight of 10mm of post in negligible.
For error, resale, and also changes in saddles, shoes, pedals, crank, etc., which can affect how much post you need.
JiveTurkey is offline   Reply With Quote
Old 03-31-12, 06:09 PM   #7
FastJake
Constant tinkerer
 
FastJake's Avatar
 
Join Date: May 2010
Location: Madison, Wisconsin
Bikes:
Posts: 7,574
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by hueyhoolihan View Post
i'm kind of sensitive about excess weight on my bikes, but even I might hesitate to cut just 50mm.
Same here. I'm a bit of a weenie in that I like to know what everything weighs, but I won't sacrifice other things like useability or function to save weight. The only reason I'd cut down a post is if it didn't fit all the way in the frame.

How much would you save on ~100mm of post? 50g maybe?
FastJake is offline   Reply With Quote
Old 03-31-12, 06:23 PM   #8
davidad
Senior Member
 
Join Date: Feb 2009
Bikes:
Posts: 4,833
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Quote:
Originally Posted by hueyhoolihan View Post
i'm kind of sensitive about excess weight on my bikes, but even I might hesitate to cut just 50mm.
Are you sensitive about excess weight on your bike's motor?
davidad is offline   Reply With Quote
Old 03-31-12, 07:29 PM   #9
onespeedbiker
Retro Grouch
Thread Starter
 
onespeedbiker's Avatar
 
Join Date: Oct 2007
Location: Santa Cruz
Bikes: Yes
Posts: 2,210
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by cyclist2000 View Post
Why cut it at all? Leaving it full length helps resale possibilities.
The seatpost is a close fit so I figure the shorter the better; weight hasn't even a consideration. Besides I have several longer seatposts that will fit if I ever want to sell the bike; but this one is special to me.


BTW, I am retired with a nice pension and have 19 bikes in my garage. I have only sold one bike ever, which was an old Nishiki my 10 YO son excitedly found rusting in front of a house saying "Take me and give me some love" and he charged me with fixing it up. I turned the bike into fixie including lots of old school parts I had laying around, powder coating, stainless steel spokes and a fixie hub. One of my riding worked with a guy who wanted a fixie in a bad way. I showed him the bike just to show how you can build one up and it was love at first sight; who was I to stand between them?
Attached Images
File Type: jpg nitto_s83_seatpost.jpg (20.0 KB, 110 views)

Last edited by onespeedbiker; 03-31-12 at 07:36 PM.
onespeedbiker is offline   Reply With Quote
Old 03-31-12, 08:40 PM   #10
Kimmo
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Bikes: copy/paste links: http://velospace.org/node/36949 http://velospace.org/node/47746 http://velospace.org/node/47747
Posts: 7,099
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by hueyhoolihan View Post
i'm kind of sensitive about excess weight on my bikes
In that case, when you cut the tube, cut it on an angle to maximise the removed material.

I wouldn't go much past what would be level when it's inserted, though.
Kimmo is offline   Reply With Quote
Old 04-01-12, 01:31 AM   #11
conradpdx
Senior Member
 
conradpdx's Avatar
 
Join Date: Sep 2011
Location: Portland Oregon
Bikes: 70"s Raleigh Superbe, 1959 Murray Vanguard Middle weigh cruiser
Posts: 301
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I had short stem on my bike once, and rather than getting a new one, I took it past the max lines.

One day while riding to work, riding with no hands on the handle bars, I couldn't help but laugh as my butt hit the ground and the bike kept rolling on as if nothing happened. Man, I had that bike dialed in, it went at least thirty yards before it fell over.

Lucky for me and my bike it wasn't a busy street, and no cars were driving by at the time.

So I'd just recommend making sure that you don't take too much off if you cut it down.
conradpdx is offline   Reply With Quote
Old 04-01-12, 01:57 AM   #12
Kimmo
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Bikes: copy/paste links: http://velospace.org/node/36949 http://velospace.org/node/47746 http://velospace.org/node/47747
Posts: 7,099
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by conradpdx View Post
I had short stem
This confused the hell out of me until I realised you were referring to the seatpost...

The stem is the bit connecting the bars to the forks.
Kimmo is offline   Reply With Quote
Old 04-01-12, 09:22 AM   #13
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: 28,776
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 36 Post(s)
Cutting off the excess length is no problem and easy with an decent fine tooth hacksaw and you don't even have to worry about the cut being exactly 90° they way you would with a steerer.

Insert the seatpost into your frame and mark it at the desired saddle height. Then remove it and measure the distance from the end of the post to the minimum insertion line (typically 60 to 75 mm). Add that distance below the mark you made on the installed post and cut a few cm below that for some future adjustability.

I have cut down a couple of 350 mm Easton aluminum MTB posts to 250mm, which is still about 50 mm longer than I need, using a hacksaw and a steerer cutting guide (because I happen to have one) and saved 60 grams on a 31.6 mm seatpost.

Now, before anyone asks why I didn't just buy a road seatpost to begin with, I couldn't find decent quality two-bolt road posts in the diameters I needed at reasonable cost and Jenson had the Easton MTB posts on sale at a not-to-be passed up sale price.
HillRider is offline   Reply With Quote
Old 04-01-12, 11:10 AM   #14
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Bikes: 7
Posts: 18,854
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 224 Post(s)
Only if the braze-ons in the seat tube prevent getting the saddle low enough,
should sawing off the seat post be considered,

there is a dont go above this mark on many seat posts,

rule of thumb
it needs to insert below the bottom of the seat tube/top tube join .
fietsbob is online now   Reply With Quote
Old 04-01-12, 11:14 AM   #15
Kimmo
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Bikes: copy/paste links: http://velospace.org/node/36949 http://velospace.org/node/47746 http://velospace.org/node/47747
Posts: 7,099
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by fietsbob View Post
Only if the braze-ons in the seat tube prevent getting the saddle low enough,
should sawing off the seat post be considered,
Bah
Kimmo is offline   Reply With Quote
Old 04-01-12, 04:07 PM   #16
onespeedbiker
Retro Grouch
Thread Starter
 
onespeedbiker's Avatar
 
Join Date: Oct 2007
Location: Santa Cruz
Bikes: Yes
Posts: 2,210
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by conradpdx View Post
I had short stem on my bike once, and rather than getting a new one, I took it past the max lines.

One day while riding to work, riding with no hands on the handle bars, I couldn't help but laugh as my butt hit the ground and the bike kept rolling on as if nothing happened. Man, I had that bike dialed in, it went at least thirty yards before it fell over.

Lucky for me and my bike it wasn't a busy street, and no cars were driving by at the time.

So I'd just recommend making sure that you don't take too much off if you cut it down.
Believe me this was a serious concern, but my situation is quite different. The amount of seatpost I need is only 80mm above the crown. I cut the 300mm post down to 200mm; there is 120mm of post in the seat tube. Speaking of max lines, Nitto seems to have a lot of faith in seat tubes as the max line on the 300mm post is only 65mm; looking at it it just didn't seem to be enough (if you look at the photo I attached closely you can see the max line; it's the second line from the bottom.

Last edited by onespeedbiker; 04-02-12 at 04:23 PM.
onespeedbiker is offline   Reply With Quote
Old 04-01-12, 04:14 PM   #17
FBinNY 
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Posts: 29,421
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 94 Post(s)
Quote:
Originally Posted by onespeedbiker View Post
Believe me this was a serious concern, but my situation is quites different. The amoutn of seatpost I need is only 80mm above the crown. I cut the 300mm post down to 200mm; there is 120mm of post in the seat tube. Speaking of max lines, Nitto seems to have a lot of faith in seattubes as the max line on the 300mm post is only 65mm; looking at it it just didn't seem to be enough (if you look at the photo I attached closely you can see the max line; it's the second line from the bottom.
65cm is plenty of insertion depth for a post into a tube. It exceeds 2 diameters which is the rule of thumb for the first condition of safe fit. When you see deeper insertion depths such as on certain Thomson posts, it isn't because the post would tear out of the tube. It's because the OEM customer has a seat tube that extends above the seat tube, so the minumum insertion is increased to get the bottom of the post to below the bottom of the top tube (second condition of correct fit).
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FBinNY is offline   Reply With Quote
Old 04-02-12, 03:42 PM   #18
conradpdx
Senior Member
 
conradpdx's Avatar
 
Join Date: Sep 2011
Location: Portland Oregon
Bikes: 70"s Raleigh Superbe, 1959 Murray Vanguard Middle weigh cruiser
Posts: 301
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Kimmo View Post
This confused the hell out of me until I realised you were referring to the seatpost...

The stem is the bit connecting the bars to the forks.
Yeah, sorry....was a little too amused thinking back to that incident.
conradpdx is offline   Reply With Quote
Old 04-02-12, 04:27 PM   #19
onespeedbiker
Retro Grouch
Thread Starter
 
onespeedbiker's Avatar
 
Join Date: Oct 2007
Location: Santa Cruz
Bikes: Yes
Posts: 2,210
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by FBinNY View Post
65cm is plenty of insertion depth for a post into a tube. It exceeds 2 diameters which is the rule of thumb for the first condition of safe fit. When you see deeper insertion depths such as on certain Thomson posts, it isn't because the post would tear out of the tube. It's because the OEM customer has a seat tube that extends above the seat tube, so the minumum insertion is increased to get the bottom of the post to below the bottom of the top tube (second condition of correct fit).
So is minimum insertion meant to be measured at the top of the seat tube or in the seat tube even with the top tube.
onespeedbiker 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 10:20 AM.