Alu seat post / carbon frame.

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Valleyz

New Member
Hi, (new member).
I've finally taken the plunge into the world of carbon bikes after many years on aluminium.

I've just got one question regarding clamping the seat-post (an alloy one) in the carbon frame.
How easy / difficult is it to damage the carbon frame by overtightening the seat clamp?

I'm not heavy-handed and always tend, if anything, to under-tighten stuff, but I keep seeing conflicting advice: Some people seem to think carbon is as fragile as glass, others that the clamp bolt will probably fail long before the frame does.
I see lots of horror stories about carbon seat posts, but not much about alloy posts in carbon frames.

What are people's real-world experiences?
(I am using carbon paste to avoid future seizing-issues.)

Thank you :-)
 

Slioch

Guru
Location
York
How easy / difficult is it to damage the carbon frame by overtightening the seat clamp?

Very easy, I would imagine.

I learned the hard (and expensive) way, so a few years ago I invested in a torque wrench, googled the relevant settings to use for the different bits of the bike, and have stuck to it religiously ever since. I bought this one, although similar may be available on Ebay etc for less.

Oh, and :welcome: to the forum.
 

CXRAndy

Guru
Location
Lincs
Get a low range torque wrench 1-15Nm. If the bolt requires 4Nm set it to 2 and use it to tighten a bigger bolt a few times so it warms up then tighten the bolt you want
 

Smokin Joe

Legendary Member
You would have to be seriously ham fisted to do any damage. The frame is braced against the seat post when you tighten it and I can't see what harm you'd do with just hand pressure on a standard Allen key. I'd bet you'd strip the thread on the bolt long before there was any danger, bearing in mind most clamps now use a small diameter bolt.
 

Slioch

Guru
Location
York
You would have to be seriously ham fisted to do any damage. The frame is braced against the seat post when you tighten it and I can't see what harm you'd do with just hand pressure on a standard Allen key. I'd bet you'd strip the thread on the bolt long before there was any danger, bearing in mind most clamps now use a small diameter bolt.

Can you give it a go on one of your bikes and report back please ^_^

Seriously though, I used to belong to the school of thought that believed tightening bolts as much as humanly possible was the correct way of doing things. Fortunately I never got as far as trashing a frame, but I did strip a few allen bolt heads.
 

Smokin Joe

Legendary Member
Can you give it a go on one of your bikes and report back please ^_^

Seriously though, I used to belong to the school of thought that believed tightening bolts as much as humanly possible was the correct way of doing things. Fortunately I never got as far as trashing a frame, but I did strip a few allen bolt heads.
I have tightened up to the recommended max of 6Nm using a torque wrench and I stripped two bolts in the process. I don't know the M size of the bolts but they were the standard size used on clamps now and apparently they take a max torque of 5.2 Nm. Someone more knowledgeable will correct that figure if it's wrong.

Unless you are exceptionally ham fisted and built like a weight lifter without any sense of feel what you use as normal tightening pressure will do no harm.
 

Globalti

Legendary Member
Hex keys are manufactured to a certain length for a reason - so that you can't over-tighten the bolt using just the fingers that fit on the key and moderate pressure.
 

youngoldbloke

The older I get, the faster I used to be ...
Hex keys are manufactured to a certain length for a reason - so that you can't over-tighten the bolt using just the fingers that fit on the key and moderate pressure.
Yes, but you can buy long ones so how does that work?
F0734927-01.jpg
 

Soltydog

Legendary Member
Location
near Hornsea
I had a planet x carbon frame that cracked on the seatpost tube within 1 month & 500 miles :sad: IIRC the recommended torque setting was 6nm, I used my torque wrench set at 5nm :blush: But maybe I was just unlucky ?
 
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