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Bike Wing Conspiracy
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Discussion Starter · #1 ·
How much of the seat post needs/should be inside the seat tube to maintain a safety margin?

I had to buy a seat post and seat on the fly years ago after someone walked off with mine.

The only replacement I could find was what I considered long.

I recently moved back to NYC from Portland OR and had to dissasemble the bike and realized how long the damn thing is. I am thinking of cutting it; not for weight, but because it took so long to get the damn thing out of the seat tube.

So how much should be maintained inside the seatube?

The post and seat in the pic is what they got away with.
 

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I've heard all different formulas for this, but here's the conservative on for the model post you're using:

Measure the current minimum insertion line from the bottom of the post. Make sure you have at least that amount in the frame. I'd ad a little in case you ever need to move you saddle up.
 

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I am thinking of cutting it; not for weight, but because it took so long to get the damn thing out of the seat tube
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It shouldn't take more than a few seconds ot get it out no matter how long it is. The problem is that the post and the inside of the tube were not cleaned and greased properly before the post was installed.
 

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Bike Wing Conspiracy
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Discussion Starter · #4 ·
Point taken.

JCavilia said:
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It shouldn't take more than a few seconds ot get it out no matter how long it is. The problem is that the post and the inside of the tube were not cleaned and greased properly before the post was installed.
In my defense though, the post is ridiculously long.
 

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onespeed said:
In my defense though, the post is ridiculously long.
Maybe it's so tight because it's crammed down to where the tube starts to bend.

Anyway, rx advised right: go by the minimum-insertion line. If you have that much in, you should be fine. You can measure the way he suggested, or alternatively get the same result by measuring the distance from your insertion level to the minimum line, then cutting that amount off the bottom.
 

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Cheese is my copilot
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I'd leave it a little long. And I'd go with at least 2" below the TT. Some bikes (though not the one you pictured) have the seat tube extending above the TT in which case, IMO, the seat post needs to be in more than the minimum insertion line may suggest.
 

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The CPSC rule in the US is that the seatpost must be inserted two diameters of the seatpost into the frame. If it's a 27.2 mm seatpost, it must extend 54.4 mm into the frame, which is 2 1/8".
 

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Another guideline that has always made some sense to me is that the post should extend a bit (about 4 cm / 1.5 ") beyond and downward of the seat tube-to-seat stay junction to avoid stressing that frame area too much by a "working" seat post end.
 

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huvia ja hyötyä
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Seat posts manufacturers mark their minimum insertion spec on the post. I am sure there's a line on your post, 10 cm or a bit less from the bottom. That is the minimum they recommend for your post.

To protect the frame, the post should extend below the lower edge of the top tube joint, but that is a bit hard to determine on your frame. Go for 10 cm, at least, to be safe.
 
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