carbon seatpost length? how much do you need in the seat tube?

Discuss light weight issues concerning road bikes & parts.
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themidge
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by themidge

GothicCastle wrote:
Mon Nov 12, 2018 5:04 am
This is a dumb way to save almost no weight.
No it isn't, it's an easy way to save a good chunk of weight (I saved 32g by chopping off 10mm) that otherwise serves no purpose.

by Weenie


mattr
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Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

themidge wrote:
Mon Nov 12, 2018 6:52 pm
No it isn't, it's an easy way to save a good chunk of weight (I saved 32g by chopping off 10mm) that otherwise serves no purpose.
steel post? Or crap scale.


WILLIAMDENYS
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Joined: Fri Aug 24, 2018 5:06 pm

by WILLIAMDENYS

themidge wrote:
GothicCastle wrote:
Mon Nov 12, 2018 5:04 am
This is a dumb way to save almost no weight.
No it isn't, it's an easy way to save a good chunk of weight (I saved 32g by chopping off 10mm) that otherwise serves no purpose.
Carbon or alloy seatpost?


Verzonden vanaf mijn iPhone met Tapatalk
- ridley fenix sl 105 - not lightweight
- sworks tarmac sl 5 r8050 di2 - vision tc 24 wheels = 7,1kg

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themidge
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Joined: Fri Jan 13, 2017 4:19 pm
Location: underneath sweet Scottish rain

by themidge

^^ :roll:
But since you asked:
Image
I'd take those weight savings any day, and I still have more than 10cm in the seat tube.
I think, perhaps, I'm taking this side quest too seriously :D.

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573
Posts: 334
Joined: Wed Sep 05, 2012 2:38 pm
Location: West Sussex, UK.

by 573

themidge wrote:
Mon Nov 12, 2018 6:52 pm
GothicCastle wrote:
Mon Nov 12, 2018 5:04 am
This is a dumb way to save almost no weight.
No it isn't, it's an easy way to save a good chunk of weight (I saved 32g by chopping off 10mm) that otherwise serves no purpose.
Agreed, you're removing something that's just suspended in free space within the frame serving no purpose. I've cut plenty.

As an example:

3T Dorico Ltd 27.2
Standard weight: 189g
Cut weight: 146g


Hylix Carbon 25.4
Standard weight: 173g
Cut weight: 145g

NickJHP
Posts: 243
Joined: Wed Feb 14, 2018 2:22 am
Location: Canberra, Australia

by NickJHP

My Open U.P.P.E.R. frame has what the manufacturer refers to as the SafePost Pilot hole in the seat tube. It's 10cm below the top of the seat tube, with the instructions saying that the seatpost should extend at least as far as this hole so that the seat tube is properly supported:

Image

alcatraz
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Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Depends on your weight and how reinforced the seatpost and seat tube are. If you are a heavier gentleman you ought to error on the side of caution.

Setting a minimum insertion point is a bit lazy grouping all seatposts and rider weights together I think. :)

If your seatpost is a bit flexier, maybe it puts less stress on the seat tube and thus can be shorter.

If you look at a cut up frame you can see the seat tube wall thickness decreases as you move down towards the bottom bracket shell.

Maybe if the wall thins out too quick the fracture happens there? I'd like to see some pics of frames with seat tube damage.

Another thing that can happen is simply not knowing where your seatpost ends. I remember buying an integrated seat+post for a great price and noticing upon install it only goes in around 9cm. After that I remember raising the seat height by tiny increments maybe 3 times. So I don't really know where I am. I should take it out and measure it, but I've ridden around plenty and it has passed the test. I could be one of the riders with iminient failure waiting around the corner. I'm 65kg.

Catagory6
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Joined: Thu Feb 09, 2017 2:36 am

by Catagory6

GothicCastle wrote:
Mon Nov 12, 2018 5:04 am
Catagory6 wrote:
Mon Sep 17, 2018 12:53 am
want to cut down a carbon seatpost...
Good God, why? This is a dumb way to save almost no weight.
because its a 400mm post that is almost down to the upper bottle cage bolt, and i was wondering if that much post is needed inside the frame
but i guess its only a matter of a dozen or so grams. so i guess its not too important

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wheelsONfire
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Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

I would like to see any bike that has a thinner wall than Ax Lightness Vial EVO.
I have never seen that in my 44 years.
It has 10cm as minimum.
When i have asked the question where it hasn't been mentioned (minimal insert), i was told it's 10cm.
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

Karvalo
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Joined: Fri Aug 10, 2018 6:40 pm

by Karvalo

mattr wrote:
Mon Sep 17, 2018 6:49 am
I usually work on about 10cm to be on the safe side. Most marked minimum insertions i've measured over the years have been around that.
Most seatposts are marked around 6 to 8cm minimum. For some frames 10cm is more than the maximum recommended insertion, strangely enough.

mattr
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Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Must confess the last post of my own that I needed to cut was an ITM millennium. When they were still brand new and not widely available.

Does that date me?

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