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Old 08-10-11, 04:35 PM   #1
beezaur
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Past Minimum Insertion on Seatpost

An old mountain bike is past minimum insertion on the seatpost by about an inch when I put the saddle high enough.

The post measures 1.064" (27.0 mm) and extends about 8" out of the frame.

I had no lock searching here or finding a longer seatpost. Or, figuring out what to order anyway.

Could someone please explain how seatpost measurements work?
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Old 08-10-11, 05:17 PM   #2
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I don't know how the measurements work, but pulling that much too much out is asking for trouble. Did you look at Nashbar and the other on line sites for a longer seat post?
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Old 08-10-11, 05:23 PM   #3
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Check Price Point, too. But before you do that, read the side of the seatpost to find out your size.

8" post? That's about 400mm, good luck finding one appreciably longer...........
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Old 08-10-11, 05:38 PM   #4
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I'm not sure how these are measured. The post says 27.2 mm dia.

From the rails to the end of the post is 11-3/4", or 300 mm. The minimum insertion mark to the end is 4". I would have 3", which I agree is asking for trouble.
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Old 08-10-11, 06:14 PM   #5
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Google or call the LBSs for "27.2 x 400 mm seatpost".
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Old 08-10-11, 06:15 PM   #6
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They make 27.2 x 350 and 400mm seatposts. Time for a new seatpost.
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Old 08-10-11, 06:16 PM   #7
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So . . . 350 mm or 400 mm . . . how is that measured? Is that the total length of the post?
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Old 08-10-11, 07:45 PM   #8
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You measured 300mm - that's one of the standard sizes. The next size larger from what you have should be just right for you. 350-400, as suggested previously.

Seat post length is measured "from the bottom of the post to centerline of the seat rails." I seen that on the internet.
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Old 08-10-11, 08:38 PM   #9
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Thanks guys. Off to da bike store . . .
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Old 08-11-11, 01:37 AM   #10
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Quote:
Originally Posted by DX-MAN View Post
Check Price Point, too. But before you do that, read the side of the seatpost to find out your size.

8" post? That's about 400mm, good luck finding one appreciably longer...........
Just in case it becomes important to the OP or anyone else, 8" is nowhere close to 400mm. 8" is almost exactly 200mm. 400mm is about 15 3/4". I did it the easy way and pulled out the old English/metric tape measure. Makes a really dandy rough calculator.
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Old 08-11-11, 04:28 AM   #11
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I might pull a seat post a 1/4"-1/2" past the minimum mark, but no more and I would rather not. Depending on the type of bike, strength/weight of the rider and the frame composition even that small amount could be too much. Get a longer seat post.

Aaron
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Old 08-11-11, 11:25 AM   #12
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For safety's sake long seat post should start to lean towards solid bar stock rather than tubing.

I know, I've just been down that road.

Rode out, walked back with a bent seat post.
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Originally Posted by krazygluon
Steel: nearly a thousand years of metallurgical development
Aluminum: barely a hundred, which one would you rather have under your butt at 30mph?
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Old 08-11-11, 11:44 AM   #13
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I just noticed last week that I've been riding for over two years with my seat post almost an inch beyond the minimum insertion point. Maybe I should think of getting a longer seat tube?
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Old 08-11-11, 11:56 AM   #14
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People have broken off the end of the frame's , seat-tube, by riding with the post
up past the max height line..

it needs to extend into the frame past the lower side of the top tube join.

I found a proper diameter 2 bolt Campag seat post,
but it was to be to far extended, when I built my sloping top tube touring frame.

solution was buy a similar OD Kalloy post, have the OD and ID
of the 22.2 end of the post machined , sleeved to fit together,
then welded together, and machined the aluminum bead back down
to the same OD of the rest of the seat post..

2 bolt Campag seat posts and brooks leather 2 rail saddles
are made for each other.
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Old 08-11-11, 12:20 PM   #15
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Quote:
Originally Posted by Nightshade View Post
For safety's sake long seat post should start to lean towards solid bar stock rather than tubing.

I know, I've just been down that road.

Rode out, walked back with a bent seat post.
http://physics.stackexchange.com/que...ar-of-same-o-d

A hollow tube will have nearly all of the strength of a solid bar for a fraction of the weight. The fact that you bent one probably has to do with how it was damaged or a manufacturing defect.
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Old 08-11-11, 01:05 PM   #16
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Quote:
The post measures 1.064" (27.0 mm) and extends about 8" out of the frame.
Have used a Chrome Moly steel tube seatpost , with 12 of its 18 inch length sticking up.

SBS/ Red Line makes them available, 1" OD, a machined shim with the 25.4mm ID
and the proper OD to match the inside diameter of the Frame's seat tube
is available , so the solution to the OP's situation is just a trip to the Bike Shop.
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Old 08-11-11, 04:07 PM   #17
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Quote:
Originally Posted by Brontide View Post
http://physics.stackexchange.com/que...ar-of-same-o-d

A hollow tube will have nearly all of the strength of a solid bar for a fraction of the weight. The fact that you bent one probably has to do with how it was damaged or a manufacturing defect.
True to a point. What is unknown here is.......the riders weight, riders riding style (rough or easy), how long outside of frame etc.

That said, tube wall thickness also plays a huge role in tube strength. Most cycle stuff is thin wall tubing so it really isn't all that strong.

I'm a BIG fella so in order to get a safe solid seat post for my Cruiser I went to a solid 7/8" stainless steel bar stock post. It will not bend under my weight.

Sure I know that a bar stock post is sinful heavy but it's a choice....ride safe or ride with a post that might bend or break poking you know where!!
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Originally Posted by krazygluon
Steel: nearly a thousand years of metallurgical development
Aluminum: barely a hundred, which one would you rather have under your butt at 30mph?
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Old 08-11-11, 08:27 PM   #18
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I don't worry about the seat post breaking I worry more about the frame on the bike splitting out.

Aaron
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RIDE, YOU FOOL, RIDE!"
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