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 Post subject: Seatpost Question
PostPosted: Tue Jun 23, 2009 4:53 pm 
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Joined: Fri Jul 25, 2008 4:12 pm
Posts: 115
Location: Chicago, IL USA
With the new fad being an integrated post, I was thinking of the following.

I have a CAAD9 currently, and the only post I had laying about was a Thomson Elite 410mm. So right now, I've probably got 10CM that I could chop off it for weight savings.

Here's the question. Does having a longer post like that produce the same effect of having an ISP type frameset??

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 Post subject: Seatpost Question
Posted: Tue Jun 23, 2009 4:53 pm 


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 Post subject: Re: Seatpost Question
PostPosted: Tue Jun 23, 2009 7:27 pm 
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Joined: Sun Sep 10, 2006 6:43 pm
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Location: Copenhagen, Denmark, Earth, Universe
Maybe dumb question, but what effect are you talking about?


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 Post subject: Re: Seatpost Question
PostPosted: Tue Jun 23, 2009 7:35 pm 
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Location: Chicago, IL USA
Not dumb at all. I thought one of the benefits of this was to produce a stiffer platform... or not so much?

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 Post subject: Re: Seatpost Question
PostPosted: Wed Jun 24, 2009 7:42 am 
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Joined: Fri May 25, 2007 6:43 pm
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The stiffness of the frame/post interface is only affected by the actual bit of the post which touches the inside of the seat tube, probably about 8-10cm in most double butted or CF frames. If you can be bothered you can probably see/feel where the step change in internal diameter is. Any post sticking out below this point is useless. Some frames/posts with poorer tolerancing may only contact properly over 1/2 of this length as the clamp will not take up the gap between the ID and OD all the way down to the diameter change.

So no, having a longer than needed seatpin won't give you the effect you think you'll get.


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 Post subject: Re: Seatpost Question
PostPosted: Wed Jun 24, 2009 1:32 pm 
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Joined: Fri Jul 25, 2008 4:12 pm
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Location: Chicago, IL USA
Ah. That makes sense. I didn't even think of the fact that the tube lengths change.

Now... where did I put my hacksaw. That thing's gettin' chopped today!

Thanks for the replies!

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 Post subject: Re: Seatpost Question
PostPosted: Wed Jun 24, 2009 1:42 pm 
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Careful you don't chop too much or you will end up with below minimum insertion and end up with a snapped/cracked frame.

Measure 26 times, check a further 5 or 6, sleep on it, measure a couple more times, then cut.


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 Post subject: Re: Seatpost Question
PostPosted: Wed Jun 24, 2009 2:18 pm 
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Joined: Fri Jul 25, 2008 4:12 pm
Posts: 115
Location: Chicago, IL USA
Thanks...

I was going to measure the minimum insertion line from the bottom of the post to the line and leave one cm more than that distance when I chop.

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 Post subject: Re: Seatpost Question
Posted: Wed Jun 24, 2009 2:18 pm 


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 Post subject: Re: Seatpost Question
PostPosted: Wed Jun 24, 2009 3:19 pm 
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Location: Drenthe, Holland
A very good rule of thumb is to let the post extend one inch past the underside of the toptube and then cut what is left.

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