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...idios...
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"It'll be marked on the seatpost"

That'll cover the pin, but your frame might have different ideas! There should be a small hole (2mm) drilled in the frame which lets you see when the pin is inserted to the minimum acceptable for the design of the frame.
Find out how much pin you must have in the frame before you consider anything else.

Edit: that's quite possibly all irrelevent. You're riding a hardtail, yes? Then like earl06 said, it should be marked on the post...hmm.
 

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This is an email I received from Sherwood Gibson, owner and operator of Ventana Mountain Bikes:

I recommend 4" as a minimum insertion on seat posts. This will get you to start of the flared section of the seat tube and will give you maximum strength and stiffness. The minimum insertion point marked on the seat post is for the survival of the post, not the frame. Most people don't take this into account.
FYI - all of Sherwood's frames are aluminum.
 

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1946:2006:2066
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1,458 Posts
still not good enough

The seat post must be inserted far enough to pass beneath the bottom of the
seat tube to top tube weld. In the absence of a ST/TT gusset the seat post
should be inserted 10mm to 20mm past this weld. Consider the Ventana
El Fuego vs the El Saltamontes as examples of the differences. One without
a gussest and one with a gusset.

michael
 

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3 "fiddy" for short
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2,739 Posts
FireDog46 said:
The seat post must be inserted far enough to pass beneath the bottom of the
seat tube to top tube weld. In the absence of a ST/TT gusset the seat post
should be inserted 10mm to 20mm past this weld. Consider the Ventana
El Fuego vs the El Saltamontes as examples of the differences. One without
a gussest and one with a gusset.

michael
On a lot of frames the seattube flares internally after several inches. Therefore, you could insert a post as far as you want, but will only be as sturdy as the unflared section of the seattube allows it to be.

You are correct in saying that the deeper you go the better off you would be, but there is a point where extra post does no good.

I guess it depends on the frame as to the amount of seattube that is needed. I was just saying that Turner recommends 4", or more, due to the seattube flaring.
 

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1946:2006:2066
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1,458 Posts
The term "flaring" was confusing me.

What they mean is the end of the "butted" portion of the seat tube.
Beyond that the seat post isn't making contact with the seat tube.

Here is a rather lenghty thread of what happens if you get it wrong.
http://forums.mtbr.com/showthread.php?p=2277271#poststop
Note that Rocky Mountain spec's minimum as 100mm for us metric canucks.

michael
 
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