Cutting Seatposts

[Chris Garwood]

Hi All

Quick question, but where you are cutting a seatpost there is a formula for working out what the min
insert should be or something, isn't it like 3.5 times the diameter ?

Thanks in advance

Cheers

Chris

--
=========================================
"Pppplllleeeaaaseee Stop" - NPS Marshal

http://www.mtbbikes.co.uk

 

[Technician]

In article <[email protected]>, [email protected] says...
> Hi All
>
> Quick question, but where you are cutting a seatpost there is a formula for working out what the
> min insert should be or something, isn't it like 3.5 times the diameter ?
>
> Thanks in advance
>
> Cheers
>
> Chris
>
> --
> =========================================
> "Pppplllleeeaaaseee Stop" - NPS Marshal
>
> http://www.mtbbikes.co.uk
>
>
>

The method i used when sizing my new post was to measure the original min insertion length, cut the
post and then measure up the post and scrape a ring of paint off at the previously measured length.
i then of course use a very fine brush and some white epoxy paint to fill in the paint scratch (the
post is black).

There may be some formula to do it correctly, i just figured this was the safest way to go.

~Travis
--
To reply by email, remove clothes.

travis5765.homelinux.net, Primary Administrator TF Custom Electronic, Owner/Founder/Developer
(current project: Automotive exhaust flame-thrower)

 

[Gary In Va]

"Chris Garwood" <[email protected]> wrote in message
news:[email protected]...
> Hi All
>
> Quick question, but where you are cutting a seatpost there is a formula
for
> working out what the min insert should be or something, isn't it like 3.5 times the diameter ?

At least make sure the post extends a couple inches below where the top tube is welded to the
seat tube.

Gary in VA

 

[John G]

Chris Garwood wrote:
> Hi All
>
> Quick question, but where you are cutting a seatpost there is a formula for working out what the
> min insert should be or something, isn't it like 3.5 times the diameter ?

It depends.. Some seatposts are internally butted and cutting them down could compromise it's
integrity.

Unless you are riding a "Y" frame type, full squish and the seat-post is hitting the tire, why would
you want to cut it?

 

[Andrew]

"John G" <[email protected]> wrote in message news:[email protected]...
>
>
> Chris Garwood wrote:
> > Hi All
> >
> > Quick question, but where you are cutting a seatpost there is a formula
for
> > working out what the min insert should be or something, isn't it like
3.5
> > times the diameter ?
>
> It depends.. Some seatposts are internally butted and cutting them down could compromise it's
> integrity.
>
> Unless you are riding a "Y" frame type, full squish and the seat-post is hitting the tire, why
> would you want to cut it?
>
to shave 2.4567 grams and be able to eat one more dozen of donuts without messing up the weight to
power relation.

 

[Bill Wheeler]

On Mon, 21 Apr 2003 10:10:13 -0400, John G <[email protected]> wrote:

>Unless you are riding a "Y" frame type, full squish and the seat-post is hitting the tire, why
>would you want to cut it?

'cause it's kewl to cut down parts. I hear there are a few riders in this NG who even cut down there
handlebars, (can't have a extra 1 inch sticking out or some other dumb sh!t reason).

Possible a weight saving measure, this may actually save and oz. or a couple of grams.

Or perhaps they bought the wrong length post and lost the receipt.

Dunno Clyde, jus' dunno.

Bill The mind serves properly as a window glass rather than as a reflector, that is, the mind should
give an immediate view instead of an interpretation of the world.
:-]

 

[Jan Sacharuk]

In article <[email protected]>, Bill Wheeler wrote:
> 'cause it's kewl to cut down parts. I hear there are a few riders in this NG who even cut down
> there handlebars, (can't have a extra 1 inch sticking out or some other dumb sh!t reason).
>
> Possible a weight saving measure, this may actually save and oz. or a couple of grams.

Sometimes, having a couple kilometres of post is just a pain. Why do you want a really long post if
you aren't using a bunch of it? Why do people cut the cables to the right length instead of leaving
an extra 30cm at the end just in case?

JS

--
========================= [email protected] ========================
Jan Sacharuk Member in Good Standing of The Discordian Solidarity Turn on viewing of the X-Geek-Code
header to see my Geek Code
-----------------------------------------------------------------
Of course this is the best of all possible worlds. I'm in it. -Solomon Short

 

[Eric Lafferty]

John G wrote:

> Chris Garwood wrote:
> > Hi All
> >
> > Quick question, but where you are cutting a seatpost there is a formula for working out what the
> > min insert should be or something, isn't it like 3.5 times the diameter ?
>
> It depends.. Some seatposts are internally butted and cutting them down could compromise it's
> integrity.
>
> Unless you are riding a "Y" frame type, full squish and the seat-post is hitting the tire, why
> would you want to cut it?

Lots of reasons.

In my case it was because the LBS only stocked a 410mm post in the diameter I needed. The post
worked fine, but if I lowered it about 1" it hit an obstruction in the seat post where the
rear suspension was welded to the seat post. I wanted most adjust ability so I cut the 410mm
post to 350mm.

I'm sure that others have reasons too. It's easy enough to do so what's the big deal?

For Thomson posts the minimum insertion is 100mm. I made sure that I have at least that much in the
frame after the cut was made.

 

[Jonathan Bond]

John G wrote:
>
>
> Chris Garwood wrote:
>
>> Hi All
>>
>> Quick question, but where you are cutting a seatpost there is a formula for working out what the
>> min insert should be or something, isn't it like 3.5 times the diameter ?
>
>
> It depends.. Some seatposts are internally butted and cutting them down could compromise it's
> integrity.
>
> Unless you are riding a "Y" frame type, full squish and the seat-post is hitting the tire, why
> would you want to cut it?

I've been tempted to cut mine. 31.6mm diameter, 410mm length. When I drop the saddle all the way to
fit it into the trunk of my Jeep (I built a fork mount rack that works quite nicely) it hits the
downtube bottle cage bolt. it JUST fits into the car now - if I could drop it that extra two inches,
then it would fit much easier. Same for doing trialsy stuff - sometimes its nice to have a couple
more inches of clearance putzing around the campus (it also wouldn't hit my thighs as much if it was
a tiny bit lower).

i could cut off enough to make a somewhat significant weight gain, in terms of weight weeniedom. If
you're 200+ pounds, then no biggie, but when you're 135 all those little ounces here and there can
really add up. then again, I've considered putting Ti and Aluminum bolts all over my new bike, and
its getting carbon fiber spacers...

Jon Bond

 

[John G]

Eric Lafferty wrote:

> It's easy enough to do so what's the big deal?

As I stated earlier, _some_ seatposts are internally butted so they are thicker at the clamping area
and thinner elsewhere. if you are now changing the actual clamping area, you might possibly be
clamping down on an area not designed to sustain such clamping forces, and thus crush the post

 

[John G]

Jonathan Bond wrote:

> then again, I've considered putting Ti and Aluminum bolts all over my new bike, and its getting
> carbon fiber spacers...

<Pssst> hey kid <psst> wanna buy some Ti? I got some Ti innet and outter chainring bolts. Come on,
you know you wanna.... Finest kind, highest grade. Commercially pure.

--
John G. god-dam the (Ti) pusher man

 

[Bomba]

John G wrote:

> <Pssst> hey kid <psst> wanna buy some Ti? I got some Ti innet and outter chainring bolts. Come on,
> you know you wanna.... Finest kind, highest grade. Commercially pure.

Yeah, but do they stick to magnets like proper ones do?

--
a.m-b FAQ: http://www.t-online.de/~jharris/ambfaq.htm

b.bmx FAQ: http://www.t-online.de/~jharris/bmx_faq.htm

 

[Mark Hickey]

John G <[email protected]> wrote:

><Pssst> hey kid <psst> wanna buy some Ti? I got some Ti innet and outter chainring bolts. Come on,
>you know you wanna.... Finest kind, highest grade. Commercially pure.
>--
>John G. god-dam the (Ti) pusher man

Wow... I guess that makes me a ti kingpin. I need a macho nickname - how about "scarknees"?

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Mark Hickey]

Jan Sacharuk <[email protected]> wrote:

>Sometimes, having a couple kilometres of post is just a pain.

Yeah, I would imagine so... like for example, having to mount your bike with the use of a
helicopter. Plus, I'd have to believe finding a stem to get the bar height right would be a *****.
And I wouldn't want to ride it down much of a hill!

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[John G]

bomba wrote:
> John G wrote:
>
>> <Pssst> hey kid <psst> wanna buy some Ti? I got some Ti innet and outter chainring bolts. Come
>> on, you know you wanna.... Finest kind, highest grade. Commercially pure.
>
>
> Yeah, but do they stick to magnets like proper ones do?

Not even my super powered neodymium magnets!

 

[Spademan O----L]

"John G" <[email protected]> wrote in message news:[email protected]...
>
>
> Eric Lafferty wrote:
>
> > It's easy enough to do so what's the big deal?
>
> As I stated earlier, _some_ seatposts are internally butted so they are thicker at the clamping
> area and thinner elsewhere. if you are now changing the actual clamping area, you might possibly
> be clamping down on an area not designed to sustain such clamping forces, and thus crush the post
>

Am I being particularly thick or does this have no effect whatsoever on whether the post is cut or
not? if its clamping on an area it will be clamping there whether there is 3'' or 3' below it.

 

[Lee Bower]

So what you're saying is that you shouldn't adjust your seatpost to the proper height because it
could be in an area where it is butted??? What does that have to do with cutting the post that is
way down in the frame?

Lee

"John G" <[email protected]> wrote in message news:[email protected]...
>
>
> Eric Lafferty wrote:
>
> > It's easy enough to do so what's the big deal?
>
> As I stated earlier, _some_ seatposts are internally butted so they are thicker at the clamping
> area and thinner elsewhere. if you are now changing the actual clamping area, you might possibly
> be clamping down on an area not designed to sustain such clamping forces, and thus crush the post

 

[Dick]

Bill Wheeler wrote: I hear there are a few riders in
> this NG who even cut down there handlebars, (can't have a extra 1 inch sticking out or some other
> dumb sh!t reason).
>

Ever clip a tree?

 

[John G]

spademan o---[) * wrote:
> "John G" <[email protected]> wrote in message news:[email protected]...
>
>>
>>Eric Lafferty wrote:
>>
>> > It's easy enough to do so what's the big deal?
>>
>>As I stated earlier, _some_ seatposts are internally butted so they are thicker at the clamping
>>area and thinner elsewhere. if you are now changing the actual clamping area, you might possibly
>>be clamping down on an area not designed to sustain such clamping forces, and thus crush the post
>>
>
>
> Am I being particularly thick or does this have no effect whatsoever on whether the post is
> cut or not?

No, you are right in your thinking..... _IF_ you are dealing w/a butted post and youa are already
clamping in a non butted area, because it is of the wrong lenght, it matters not. Which only
underscores the necessity to purchase a post of the correct size rahter than cut it one down that is
too long.....

 

[John G]

Lee Bower wrote:
> So what you're saying is that you shouldn't adjust your seatpost to the proper height because it
> could be in an area where it is butted???

Yeah, I guess I did say that..... I blame it on the Triple Boc I had last night and lack of caffeine
this morning

>What does that have to do with cutting the post that is way down in the frame?

Apparently, nothing