Seatposts: Usable Lengths?

"PeteCresswell" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I need 32" from the seatpost's clip to the center of the
BB spindle.

A frame I'm thinking about is only 21".

Anybody know what length post I'd need to get a full 12"
(an extra inch just for margin of error...) of actual,
usable extension from the top of the seat tube to the clip
where the saddle rails lie?

Seems like post specs are something like LOA...but
not quite.

Sounds like you need a 350 mm MTB post, they're pretty
standard. If that's a little short, you can find 400 mm
posts without too much difficulty.

Thompson for will do it.

http://www.lhthomson.com/SPpartslist0.asp

On 27 Apr 2004 05:49:42 -0700, [email hidden]

(PeteCresswell) may have said:

I need 32" from the seatpost's clip to the center of the
BB spindle.

A frame I'm thinking about is only 21".

Anybody know what length post I'd need to get a full 12"
(an extra inch just for margin of error...) of actual,
usable extension from the top of the seat tube to the clip
where the saddle rails lie?

Seems like post specs are something like LOA...but
not quite.

400mm may do the trick, depending on the frame's
characteristics, but I'd go for a 420 or 450 if it was me.
400 isn't hard to find, but anything longer is rare. You may
have a bit of a challenge ahead of you.

Ballpark numbers: 400mm is a bit under 16" long. That gives
you just 4" of post inside the tube; with a lever arm that
long, I'd be nervous.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

On Tue, 27 Apr 2004 12:57:46 GMT, "Peter Cole"

may have said:

"PeteCresswell" <[email hidden]> wrote in
message
"]news:[email hidden]...

Quoted message said:

I need 32" from the seatpost's clip to the center of the
BB spindle.

Anybody know what length post I'd need to get a full 12"
(an extra inch just for margin of error...) of actual,
usable extension from the top of the seat tube to the
clip where the saddle rails lie?

Sounds like you need a 350 mm MTB post, they're pretty
standard. If that's a little short, you can find 400 mm
posts without too much difficulty.

That would give him less than 2" of post inside the tube;
that would be well below the min insert line on most posts,
and not necessarily safe even for light duty depending upon
the frame.

350mm = 13.78", leaving just 1.78" inside the seat tube, not
enough for safety on most frames. 400mm = 15.75", *maybe*
enough. Frame design will have a lot to do with it.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

"Werehatrack" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

On 27 Apr 2004 05:49:42 -0700, [email hidden]

(PeteCresswell) may have said:

I need 32" from the seatpost's clip to the center of the
BB spindle.

A frame I'm thinking about is only 21".

Anybody know what length post I'd need to get a full 12"
(an extra inch just for margin of error...) of actual,
usable extension from the top of the seat tube to the
clip where the saddle rails lie?

Seems like post specs are something like LOA...but
not quite.

400mm may do the trick, depending on the frame's
characteristics, but I'd go for a 420 or 450 if it was me.
400 isn't hard to find, but anything longer is rare. You
may have a bit of a challenge ahead of you.

Ballpark numbers: 400mm is a bit under 16" long. That
gives you just 4" of post inside the tube; with a lever
arm that long, I'd be nervous.

In this range of lengths, it doesn't matter how much more
post is inside the seat tube. If anything gives, it's the
post that is going to break directly above where it enters
the seat tube.
--
Mark South Citizen of the World, Denizen of the Net <<Tiens!
Ce poulet a une grenade!

On Tue, 27 Apr 2004 20:23:49 +0200, "Mark South"

may have said:

In this range of lengths, it doesn't matter how much more
post is inside the seat tube. If anything gives, it's the
post that is going to break directly above where it enters
the seat tube.

If I still had it, I could show you a photo of a suspension
(triangle, not Y) frame whose seat tube folded just under
the top tube. The bike had a 400mm seat post with just a bit
over 2" of the post inserted. I've also seen a cracked GT
frame (one of the ones with the silly Hellenic stays) that
was similarly abused, although only with a 350mm post. The
welds on both stays had cracked (one fully, one partway) out
of the seat tube. The owner kept hearing an odd clickety-
creak as he pedalled, and wondered what it was... (In the
frame's defense, the rider's weight was on the close order
of 260 lbs.)

Not all seat posts are going to be the weak link. Some are
quite robust.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

"Werehatrack" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

On Tue, 27 Apr 2004 20:23:49 +0200, "Mark South"

may have said:

In this range of lengths, it doesn't matter how much more
post is inside

the

Quoted message said:

Quoted message said:

seat tube. If anything gives, it's the post that is going
to break

directly

Quoted message said:

Quoted message said:

above where it enters the seat tube.

If I still had it, I could show you a photo of a
suspension (triangle, not Y) frame whose seat tube folded
just under the top tube. The bike had a 400mm seat post
with just a bit over 2" of the post inserted.

I find it surprising that the top tube didn't brace the
load. Did the welds fail too? And was this an
ultralight frame?

Quoted message said:

I've also seen a cracked GT frame (one of the ones with
the silly Hellenic stays) that was similarly abused,
although only with a 350mm post. The welds on both stays
had cracked (one fully, one partway) out of the seat
tube. The owner kept hearing an odd clickety-creak as he
pedalled, and wondered what it was... (In the frame's
defense, the rider's weight was on the close order of
260 lbs.)

Yeah, I hear you, but those frames seem to fail with short
seatposts and average rider weights too.

Quoted message said:

Not all seat posts are going to be the weak link. Some are
quite robust.

Actually, in some small way I find that reassuring - the
first failure you describe is preferable to that which
involves insertion of a sharpened seatpost end into the
rider's gluteal region.
--
Mark South Citizen of the World, Denizen of the Net <<Tiens!
Ce poulet a une grenade!

(PeteCresswell) said:

Anybody know what length post I'd need to get a full 12"
(an extra inch just for margin of error...) of actual,
usable extension from the top of the seat tube to the clip
where the saddle rails lie?

12" is 305mm. So 350mm is slightly but definitely too short.

Thomson posts come in 410mm, which is just about as short a
post as I'd consider. Those posts are amazingly strong,
though, and you can have absolute confidence in them.

IRD posts come in 425mm, but are certainly no stronger than
a Thomson post.

Chalo Colina

RE/

Quoted message said:

I'd go for a 420 or 450 if it was me. 400 isn't hard to
find, but anything longer is rare. You may have a bit of a
challenge ahead of you.

Sounds to me like I should re-spec the frame to have a 22"
seat tube instead of
21.
--
PeteCresswell

(Chalo) said:

(PeteCresswell) said:

Anybody know what length post I'd need to get a full 12"
(an extra inch just for margin of error...) of actual,
usable extension from the top of the seat tube to the
clip where the saddle rails lie?

12" is 305mm. So 350mm is slightly but definitely too
short.

Thomson posts come in 410mm, which is just about as short a
post as I'd consider. Those posts are amazingly strong,
though, and you can have absolute confidence in them.

IRD posts come in 425mm, but are certainly no stronger than
a Thomson post.

Chalo Colina

According to their website, Thomson straight 410mm posts
have to be inserted 3" into the frame, leaving 333mm from
top of seat tube to saddle rails. The layback posts have to
be inserted 4", presumably to cater for the greater torque
exerted by a vertical load being moved horizontally away
from the fulcrum, leaving 308mm out of the frame.

USE 420mm posts have a limit mark at 100mm, leaving 320mm
out of the frame.

Having used both, I prefer the Thomson

Kinky Cowboy*

*Batteries not included May contain traces of nuts Your
milage may vary

Quoted post said:

Originally posted by Petecresswell
I need 32" from the seatpost's clip to the center of the
BB spindle.

A frame I'm thinking about is only 21".

Anybody know what length post I'd need to get a full 12" (an
extra inch just for margin of error...) of actual, usable
extension from the top of the seat tube to the clip where
the saddle rails lie?

Seems like post specs are something like LOA...but not
quite.

Salsa makes a 410mm long post. Nice microadjusting system and a little less expensive then Thomson. I have owned 2 of these with no problems. But how are you going to get the bars up there or do you like 'em down low.

Steve Shapiro

PeteCresswell said:

I need 32" from the seatpost's clip to the center of the
BB spindle. A frame I'm thinking about is only 21".
Anybody know what length post I'd need to get a full 12"
(an extra inch just for margin of error...) of actual,
usable extension from the top of the seat tube to the clip
where the saddle rails lie? Seems like post specs are
something like LOA...but not quite.

As usual, when it must be unusual, there is a Nitto product
for the application. We just recived a new Nitto cold forged
post 460mm from seat rail to end, 390mm from set rail to max
line. Be sure, if your frame extends above the top tube/seat
tube joint, that your post penetrates well below the weld.
Standard MTB posts are 280mm to the limit, 360mm overall.
What is "LOA"?
--
Andrew Muzi www.yellowjersey.org Open every day since 1
April, 1971

(Pete Cresswell) said:

RE/

Quoted message said:

I'd go for a 420 or 450 if it was me. 400 isn't hard to
find, but anything longer is rare. You may have a bit of a
challenge ahead of you.

Sounds to me like I should re-spec the frame to have a 22"
seat tube instead of
21.

Definitely.

Greg

On Tue, 27 Apr 2004 20:50:32 +0200, "Mark South"

may have said:

"Werehatrack" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

On Tue, 27 Apr 2004 20:23:49 +0200, "Mark South"

may have said:

In this range of lengths, it doesn't matter how much
more post is inside

the

Quoted message said:

Quoted message said:

seat tube. If anything gives, it's the post that is
going to break

directly

Quoted message said:

Quoted message said:

above where it enters the seat tube.

If I still had it, I could show you a photo of a
suspension (triangle, not Y) frame whose seat tube folded
just under the top tube. The bike had a 400mm seat post
with just a bit over 2" of the post inserted.

I find it surprising that the top tube didn't brace the
load. Did the welds fail too? And was this an
ultralight frame?

The top tube ripped at the margin of the weld across the
top, and the lower half ot the top tube accordioned when the
seat tube folded back. The break's center showed no rubbing,
so it had not been a developing failure. The seatpost had
been in there for about a year according to the person who
had the bike, and the frame was over 6 years old. He
reported that he had looked the frame over carefully just
before the seatpost was installed, and it was definitely not
cracked then. I figured that the seat tube finally got one
impulse that distorted it to the point where it would
crease, and the whole mess failed.

I was really surprised that this happened at all on a rear
suspension frame, since the impusles shouldn't have been as
severe as they'd have been on a hardtail. On the other hand,
maybe it wasn't made using as robust of a tube set as it
might have been for a hardtail, either, and I doubt that the
maker had allowed for an underinserted long post.

Quoted message said:

Quoted message said:

I've also seen a cracked GT frame (one of the ones with
the silly Hellenic stays) that was similarly abused,
although only with a 350mm post. The welds on both stays
had cracked (one fully, one partway) out of the seat
tube. The owner kept hearing an odd clickety-creak as he
pedalled, and wondered what it was... (In the frame's
defense, the rider's weight was on the close order of
260 lbs.)

Yeah, I hear you, but those frames seem to fail with short
seatposts and average rider weights too.

So I'm told. I had a chance to pick up some of those used
recently for $10 each, and I passed them up.

Quoted message said:

Quoted message said:

Not all seat posts are going to be the weak link. Some
are quite robust.

Actually, in some small way I find that reassuring - the
first failure you describe is preferable to that which
involves insertion of a sharpened seatpost end into the
rider's gluteal region.

I quite agree, although the owner of the bike was still not
a happy camper.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

fatbelly-<< I need 32" from the seatpost's clip to the
center of the BB spindle.

A frame I'm thinking about is only 21".

Anybody know what length post I'd need to get a full 12" (an
extra inch just for margin of error...) >><BR><BR>

350mm is a very common seat post length...304mm or so is
12 inches...

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St.
Boulder, CO, 80302
(303)440-3535 vecchios.comvecchios.comOpen ↗ "Ruote convenzionali
costruite eccezionalmente bene"

Quoted message said:

What is "LOA"?

Length OverAll

Quoted message said:

But how are you going to get the bars up there or do you
like 'em down low.

I like them about saddle height.

*Supposedly*, it's going to work out with an uncut steering
tube, a 105-degree 130mm stem, and 2.5" risers.

Quoted post said:

Originally posted by Petecresswell
> But how are you going to get the bars up there or do you

Quoted message said:

like 'em down low.

I like them about saddle height.

*Supposedly*, it's going to work out with an uncut steering
tube, a 105-degree 130mm stem, and 2.5" risers.

Wow, I guess that will require a pile of spacers between the headset and the stem. That is if your steering tube is 300mm long like the new ones I've seen. Not a problem if it's steel and you are OK with the look. Are you talking about a suspension fork? They kick the front end up so you could reduce the number of spacers on top. Anyhow, the setup sounds a bit contrived. Either I'm missing something or you are getting the frame for the right price. No matter. I wish you good luck and I sincerely hope you enjoy your bike.

Steve Shapiro

"PeteCresswell" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Quoted message said:

But how are you going to get the bars up there or do you
like 'em down low.

I like them about saddle height.

*Supposedly*, it's going to work out with an uncut
steering tube, a 105-degree 130mm stem, and 2.5" risers.

If you're getting it built custom why not get it built to
the right size so you don't have to jump through hoops to
get a proper fit? I can understand 3 ft long seatposts and
vertical stems on an off the shelf frame, but custom?

Greg