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

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

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.

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

--

(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.

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.

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
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

Petecresswell 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.

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