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Carbon Post & 1.8mm shim Hack


Pikey
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So a question to the knowledgeable hubbers . Broke the Carbon seatpost on my Niner gravel bike 2 days ago . Not able to buy another post at the moment I decided to try a hack with a spare 25.4 carbon post I have .

 

The first shim I made had a lip on it so it sat on the collar but wouldn’t tightened up enough to stop the seatpost turning around . Obviously because I had to make up the 1.8mm which is my big concern here . So I made another shim from the same tin and glued it inside the shim with the lip.

 

So now it fits nice and tight and seems as if it won’t budge at all.

 

My question is this : is trying to take up the 1.8 mm with a double shim dodgy ? Am not worried about the frame as it’s steel but am about the seatpost braking mid ride . The shim does goes past where the seat stays and top tube meet probably by about 3/4cm’s . The seatpost is also inserted about 20cm’s inside the seatpost tube. The collar now sits slightly higher than the collar as can be seen in the pics .

 

Is 1.8 mm to much to take up with a shim?

With it being a gravel bike the jarring the seatpost will take is it to much ?

Is 25.4 to small for a gravel seatpost ?

 

Keen to here everyone’s thoughts .

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Edited by Pikey
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A shim's a shim, as long as it's 100mm long and the right thickness so you maintain your minimum insert and aren't just pinching the post at the clamp.

Not sure of the length of the shim need to measure it . Would guess about 8-10cm long . As for the thickness I don’t have a vernier to measure it. Best guess it’s ever so slightly to thick ,maybe .

Minimum insert of post is lower than recommended.

 

I suppose the torque of the clamp needs to be accurate so as not to pinch the post ...that’s how I broke the last one being ham fisted .

 

So most important: shim is long enough and collar torque is accurate. The 25.4 is not an issue.

 

Then all should be good.

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Edited by Pikey
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Nah. I would, but just cos I'm a perfectionist, but it's just there to stop the shim from falling down the seat tube. That missing 2mm of interface won't make any material difference.

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Nah. I would, but just cos I'm a perfectionist, but it's just there to stop the shim from falling down the seat tube. That missing 2mm of interface won't make any material difference.

That’s why I put the black tape on it so I don’t have to look at it as it bugs me .

 

Going to tap that lip to the collar now .

 

Shot for advice .

Edited by Pikey
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