Alu seat post / carbon frame.

[Valleyz]

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]

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 to the forum.

 

[CXRAndy]

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]

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]

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.

 

[davidphilips]

Just remember to use some carbon assembly paste, money very well spent.

 

[Smokin Joe]

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]

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]

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?

 

[Smokin Joe]

Yes, but you can buy long ones so how does that work?
View attachment 452137

Handy for undoing bolts that have been tightened by a gorilla.

 

[Soltydog]

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

 

[youngoldbloke]

Handy for undoing bolts that have been tightened by a gorilla.

- or ones you can't reach with a short one