Zeus seat post min insertion height?

A shy person said:

My track bike has a Zeus 26.8mm seatpost fitted
which appears to use fairly thick alu tube.

Does anyone know how much of this post I
should have below the clamp/in the frame?

The post is 180mm long and currently has
75mm inside the frame.

The usual rule of thumb is 2 1/2", so you're in fine shape.

In practice, you can often get away with quite a bit less, mainly
depending on the frame design, rider weight, and overall length of the
seatpost.

With a good quality seatpost, the issue isn't whether you'll damage the
post, but whether you'll damage the frame. If there's too little post
inside the seat tube you can distort the seat tube.

Frames with seat tubes that protrude above the top tube with no
additional support are particularly at risk for this.

Generally I would say you want to have the seat post extend into the
frame at least to the bottom of the top tube.

Sheldon "Simple Question, Complicated Answer" Brown
+-------------------------------------------+
| Good judgment comes from experience, |
| and experience comes from bad judgment. |
| --Fred Brook |
+-------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

On Sun, 16 Jan 2005 20:39:07 +1100, "hippy"

may have said:

My track bike has a Zeus 26.8mm seatpost fitted
which appears to use fairly thick alu tube.

Does anyone know how much of this post I
should have below the clamp/in the frame?

The post is 180mm long and currently has
75mm inside the frame.

In my opinion, for conventional frames, there are two answers to this.

The first one is that there is usually a "minumum insertion" mark on
the post itself; this is the amount that the maker of the *post* feels
must be inside the seat tube in order to provide a safe result.

The second answer is that no matter how far down the post you find the
minimum insertion mark, the post still needs to be deep enough in the
seat tube that the end of it is slightly past the bottom of the joint
with the top tube. I compare the post to the frame; if the post's
min-insertion line is above the clamp when the end of the post is
about 15-25mm below the top tube's lower extent, then I use the
manufacturer's mark. If the min-insertion line is below the clamp at
that point, I make a new mark on the post and use that as *my* minimum
insertion guide.

Frames with peculiar designs, and drop-frame bikes, have to be
evaluated differently, of course.

--
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 Mon, 17 Jan 2005 18:07:51 GMT, John Thompson

may have said:

Werehatrack said:

On Sun, 16 Jan 2005 20:39:07 +1100, "hippy"

may have said:

My track bike has a Zeus 26.8mm seatpost fitted
which appears to use fairly thick alu tube.

Does anyone know how much of this post I
should have below the clamp/in the frame?

Quoted message said:

In my opinion, for conventional frames, there are two answers to this.

The first one is that there is usually a "minumum insertion" mark on
the post itself; this is the amount that the maker of the *post* feels
must be inside the seat tube in order to provide a safe result.

The "minumum insertion" mark on stems and seat posts came as a result of
CPSC requirements in the late 70's. The OP's Zeus post may well pre-date
this requirement.

I have seen them on older units as well, but you are correct that they
were far from universal before the requirement went into effect, and
were quite uncommon (to the point of unheard-of IIRC) prior to the
late '60s. There may well not be one on the unit in question, that's
quite true. I had forgotten that this was not always as it is now...

--
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.