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Necessity is the mother of invention

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Necessity is the mother of invention

Old 06-11-20, 08:22 PM
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Jicafold
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Necessity is the mother of invention

So I bought an older big tube Cannondale road bike the other day. This is the seatpost that was in it. Looks like someone really needed a seatpost. Strange but true. Not sure how it is fused together but it feels solid.



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Old 06-11-20, 08:30 PM
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Originally Posted by Jicafold View Post
Not sure how it is fused together but it feels solid.
It looks to my like smaller seatpost is jammed into a bigger one? I'd want to see a closer look without the seat attached. Regardless, I would NOT ride that thing. The price of failure could be quite painful.
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Old 06-11-20, 09:18 PM
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Lots of seat posts have a press fit top onto the shaft. This looks like the top was removed (by choice or happenstance) from the OEM shaft and then reinstalled in a cut down shaft. Maybe to get a different diameter shaft?? Maybe to clear an inside the seat tube obstruction?? As long as the top stay in the shaft all will likely be good, if ugly. So the question I would ask is whether the top is well secured into the shaft, or not. From a photo we can't tell that. Andy
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Old 06-11-20, 09:22 PM
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Yes, that would be a good explanation. But no seat tube obstruction appears. Not sure if that was the original 2 bolt attachment on top or not. I have seen that pressfit type of attachment before...broken. I suspect this was some frankenbike approach to get a proper size post. I could clean, sand, wire brush, paint, etc., to make it look ok.
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Old 06-11-20, 10:07 PM
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Originally Posted by Jicafold View Post
I could clean, sand, wire brush, paint, etc., to make it look ok.
Or you could spend $20 for a new alloy post and ensure you're not anally impaled by a suspect looking component for which you have no knowledge of its history and how it's been modified.

Last edited by Rogerogeroge; 06-11-20 at 10:12 PM. Reason: apostrophe
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Old 06-12-20, 02:41 AM
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It's probably safe, although that post looks extremely short to me (check minimum insertion).

It's also extremely ugly. I'd buy a new post and replace it.
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Old 06-12-20, 07:16 AM
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So that's 3 votes for safe and 1 vote for unsafe.
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Old 06-12-20, 07:22 AM
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Originally Posted by Jicafold View Post
So that's 3 votes for safe and 1 vote for unsafe.
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Old 06-12-20, 08:33 AM
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Originally Posted by Jicafold View Post
So that's 3 votes for safe and 1 vote for unsafe.
But 3 votes to replace. I would make it 4
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Old 06-12-20, 09:13 AM
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I vote to replace the saddle. I'm present but not voting on the seat post.

Saddle looks like it has a little cusioning under the cover and if the top is rounded, I'd be uncomfortable for any ride longer than 10 miles and in pain by 30 miles.

But my butt's not yours, so you decide.
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Old 06-12-20, 09:40 AM
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A professional way to do it is a machined seat post sizing shim sleeve ..

note 2 measurements: Inside and out side diameters.
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Old 06-12-20, 09:57 AM
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I wonder if sometime in the future when riding over a big bump or pothole on the road, if that top section will get knocked down into the lower section and hide that narrower balck section, and if the saddle will pivot when that happens and cause the rider to lose control of the bike.?

To me it looks a lot like an accident waiting for a place to happen.

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Old 06-12-20, 12:18 PM
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Originally Posted by Miele Man View Post
I wonder if sometime in the future when riding over a big bump or pothole on the road, if that top section will get knocked down into the lower section and hide that narrower balck section, and if the saddle will pivot when that happens and cause the rider to lose control of the bike.?

To me it looks a lot like an accident waiting for a place to happen.

Cheers
It seems one tube is inside the other. If it slides it will slide down. A PITA, but not really dangerous.

I'd replace the post anyway. It's crap-looking.
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Old 06-12-20, 12:21 PM
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Originally Posted by Amt0571 View Post
It seems one tube is inside the other. If it slides it will slide down. A PITA, but not really dangerous.

I'd replace the post anyway. It's crap-looking.
I was thinking about if the top portion slips into the lower portion and twists a lot at the same time.

Cheers
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Old 06-12-20, 12:26 PM
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Originally Posted by Miele Man View Post
I was thinking about if the top portion slips into the lower portion and twists a lot at the same time.

Cheers
I see no reason for it to twist. I don't think it would be terribly dangerous either.

Anyway, as I said, I'd replace that POS in a pinch. A seatpost is not that expensive if you don't want something fancy.
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Old 06-12-20, 01:39 PM
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Originally Posted by Amt0571 View Post
I see no reason for it to twist. I don't think it would be terribly dangerous either.

Anyway, as I said, I'd replace that POS in a pinch. A seatpost is not that expensive if you don't want something fancy.
I figure there's a good risk of it compressing and or shifting sideways where the parts are joined. Therefore like you, I'd spend a few dollars and get a proper seatpost.

Cheers
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Old 06-12-20, 09:54 PM
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There is a lot of bad advice on this thread!
Originally Posted by Amt0571 View Post
It's probably safe, although that post looks extremely short to me (check minimum insertion).
It's probably safe??? How do you know from an internet pic? Yeah, that NTRAGER post looks short, and the bottom looks like it's been cut cleanly, so I'm sure the minimum insertion mark is valid. (Min. insertion should be atleast 2.5 times the seapost diameter for a starting point).

Originally Posted by fietsbob View Post
A professional way to do it is a machined seat post sizing shim sleeve ..

note 2 measurements: Inside and out side diameters.
^This^ is what probably should have been used to remedy the initial prob. We don't know the life story, and we're judging from a couple of internet pics.

Originally Posted by Miele Man View Post
To me it looks a lot like an accident waiting for a place to happen.
Agreed, or the OP could have just 'buffed it out'

Originally Posted by Amt0571 View Post
It seems one tube is inside the other. If it slides it will slide down. A PITA, but not really dangerous.
Um, could be very dangerous.
Originally Posted by Amt0571 View Post
I see no reason for it to twist. I don't think it would be terribly dangerous either.
Um, again, don't think? seems? probably safe? Yeah, take our word for it!
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Old 06-12-20, 10:03 PM
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I'd guess it's a 27.2 carbon post epoxied into a 31.8 or 31.6.

The epoxy is not an issue -- it's stronger than the binding force you'd get from tightening a seatpost collar.

The problems may be the length of the carbon post. And whether it was sanded down to fit.

If you can measure the inserted post and it's still 27.2 and it goes a long way -- like 5 or 6 cm -- into the alloy sleeve, the only issues will be aesthetic.

You should just be able to feel how deep it goes by running a spoke or something similar up the bottom.
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Old 06-13-20, 05:14 AM
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The mother of invention was Frank Zappa and his band. Sorry I couldn't help it.
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Old 06-13-20, 06:46 AM
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Originally Posted by ljsense View Post
I'd guess it's a 27.2 carbon post epoxied into a 31.8 or 31.6.

The epoxy is not an issue -- it's stronger than the binding force you'd get from tightening a seatpost collar.

The problems may be the length of the carbon post. And whether it was sanded down to fit.

If you can measure the inserted post and it's still 27.2 and it goes a long way -- like 5 or 6 cm -- into the alloy sleeve, the only issues will be aesthetic.

You should just be able to feel how deep it goes by running a spoke or something similar up the bottom.
It doesn't look like carbon to me. I would highly doubt that it is on an older C'dale anyway.

I tried using a 27.2->30 shim with a carbon post and a carbon frame and could never get it to hold. And yes, I used carbon paste too. I gave up and found an original post for the bike, the same as my own original, except mine stripped the ridges that held the saddle angle. It isn't a great design, nor is 30.0 a great diameter. Only Thompson makes an alloy one but I couldn't find a CF post anywhere in that size except an original.
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Old 06-13-20, 08:43 AM
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When in doubt...throw it out.
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