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#1
01-27-2008, 03:45 PM
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how long does a seatpost have to be?
I am looking at buying a 26.6mm Thomson seatpost from a forumite for use on my Gary Fisher Klunker. I dont have a photo to show, so this may not be possible to answer, BUT...
How much post needs to be inserted into the seat tube? The post May be too short, but I am not sure. As the seat sits right now, a 250mm post would leave 100mm inserted. I would be comfortable with that. The seller says the post is cut to 230mm, leaving 80mm inserted. Given that this is a rather heavy duty steel frame with a dual top tube (a klunker replica, you see) is 8cm of a Thomson posted sufficient? I weigh 200lbs, so stress loading needs to be considered. This is an odd sized seatpost, but it does come up on Ebay from time to time - should i take this one, or bide my time for a 250mm or 330mm version that will be unquestionably strong enough...? 
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#2
01-27-2008, 03:56 PM
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I've always gone by having the bottom of the seatpost at least 2" below the bottom of the top tube when inserted to desired length. I think that guideline was for mtn bikes, but the idea was to have the seatpost supported by more than just the seat tube extension.
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#5
01-27-2008, 05:01 PM
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Uuuh, I'd skip it . . .
If you're putting this on an MTB it's a whole different set of stresses when you come down from a jump or jump over a trail obstacle. The thing could bend or break and you're stuck out in the back end of nowhere with no seatpost. don't know about you, but that would certainly ruin my ride . . . I'm with SteveP. Get yourself a longer Kalloy or something from PricePoint if you can't wait around for a "name" post with the right specs to turn up on eBay.
BBD
__________________
--- __0 __0 __0 ----_-\<,_ -\<, _(_)(_)/_(_)/ (_) A thing of beauty is a joy forever--Keats
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#6
01-27-2008, 05:13 PM
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Quote:
Good Advice. 
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#7
01-27-2008, 05:46 PM
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they say it's not the length but the girth, but what do I know. . .
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#10
01-27-2008, 09:26 PM
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I agree, you guys are way wack. . .
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#12
01-27-2008, 09:31 PM
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The post definitely needs to go below the bottom of the top tube when inserted. How far below is a matter of debate. 1cm or 2cm might be enough.
I do not like Kalloy 1-bolt posts on mountain bikes. The bolts invariably break and the craddle of the seatposts ends up gently cupping ones delicate areas. I do not think I have ever seen a broken Thomson. If you run too short a post your frame will most likely break, not the seatpost.
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#13
01-28-2008, 02:17 AM
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thanks
For the record, the Klunker is never offroaded - its a commuter, so the stresses will be significantly less than mentioned.
Also, I am not so worried about breaking a post, but that I might either break a seriously cool and somewhat rare frame or break myself. That would suck - I already had a broken hand from a crash last year! My instincts tell me that 250mm is the minimum acceptable length... cheers, Darren Last edited by d_douglas; 01-28-2008 at 04:41 AM.
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#15
01-28-2008, 06:22 AM
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Quote:
"invariably"? not true. i sell many hundreds of these are i have never had one returned defective or busted. it is simple and effective and will provide long years of use. it is, in fact, a far better product than a lot of the stuff that costs far, far more.
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