minimum seat post insertion depth

I'm about to trim my seat post down. I just want to make sure there's
enough left after i'm done. How much post do i need to have in the
tube ? I've seen various numbers... But i want to be sure. Or maybe
it just doesn't matter... buaha.

Thank you,
- Captain McNerdius

My default rule is to only cut off what you need to for the post to fit.
That is, unless you're pretty sure you may want it lower in the future.
This is true for when you'll have shorter people riding it, and also if
you plan to ride on rough terrain, for instance, where you'll want a
lower seat. But in general, it's always easier to cut some more off,
than to add some on.

If the goal is to shave weight, I'd say about 2", though the real
answer probably depends on your frame design, post material, clamp size,
etc. You want plenty of tube going down past the bottom of the clamp. If
you really beat on your unicycle, keep more post in there.

Lastly, remember if you want to raise it in the future, leave room!


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My understanding is that you want enough seatpost to go at least the
diameter of the post lower than the bottom of the slot on the seat tube.
This might not be true if the seat tube has butting or reinforcement
below that point. If it is reinforced you might need to have it go the
diameter of hte seat tube past the reinforcement, otherwise it will set
up a weak spot. Personally I wouldn't cut it any shorter than I need
for the reasons stated in the prior reply.

jerry


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johnfoss;1106419 wrote:
If you really beat on your unicycle, keep more post in there


...but if this is you, don't lower it all the way so that the bottom
end of the post hits the crown inside the neck of the frame, leave a
little space like 1/2".

If you did have the post hitting the crown you would increase the
likely-hood of breaking the neck off where it meets the crown.


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Looking at the KH assembly guide this morning it suggests a minimum of
50mm of seat post in the frame.

I leave as much length as I can on the seat post i.e. cut it to the
right height for the longest crank I use, then raise the seat post from
there for shorter cranks. For me that means the seatpost only raises
~25-35mm, leaving ~70mm-80mm in the frame, depending on the uni.

If it worked out to be any less than that in the frame, I'd probably
keep a spare seat post cut to an alternative length and swap it when
swapping cranks.


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lunicycle
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I would go with about double the diameter of the seat post or more. I
don't have experience that would back this up, but my reasoning comes
from commonly used conventions with screws and fasteners and engagement
lengths that I've touched on through my schooling (engineering).

Otherwise I'd also go with leaving as much on as possible. If you need
for it to be shorter so you have this much possible variation then cut
it just enough to provide you with what you need, no more.


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disgruntleddave
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disgruntleddave;1106759 wrote:
I would go with about double the diameter of the seat post or more. I
don't have experience that would back this up, but my reasoning comes
from commonly used conventions with screws and fasteners and engagement
lengths that I've touched on through my schooling (engineering).



Yep I was just thinking the same, and for the same reason.

Always cut your post down bit by bit so you don't lop too much off and
scrap acidentally scrap it. Leave as much as you can.


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kington99

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