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Work stand and carbon seat post(12 posts)

Work stand and carbon seat posttxcross
Aug 5, 2003 1:11 PM
I have always clamped my bike by the seat post in my work stand. I am looking at getting a bike with a carbon seat post, any problems continuing to work this way or should I clamp to the seat tube/top tube instead? Frame is aluminum...

Thanks
re: Work stand and carbon seat postrrjc5488
Aug 5, 2003 1:20 PM
Not as bad as clamping it in the seat tube.
I agree.Dave Hickey
Aug 5, 2003 4:08 PM
I clamp mine to a carbon post with no problems. A seat tube clamp puts far more stress on the post.
Exact same commentpmf1
Aug 6, 2003 10:24 AM
The last thing you want to do is clamp it to the frame.

Some people are real anal and stick a different seat tube in before clamping the workstand. I've been clamping Look and Colnago carbon posts for years in my Park stand without doing any damage.

Personally, I wouldn't worry about it.
CautionBacco
Aug 5, 2003 1:30 PM
If you scratch, gouge or overstress a carbon seatpost it can fail without warning. To be safe, put an old metal seatpost on your bike while working on it.
True?jtolleson
Aug 5, 2003 5:18 PM
Scratch? I mean, I keep hearing these kinds of things but I wonder if they are true or cyclist folklore. A seatpost "fails without warning" because it was "scratched?"

A workstand clamp probably puts a lot less torque on a CF seatpost than me straining against the saddle on a steep seated climb.

I'm not trying to be argumentative, but I would really appreciate an accurate bottom line on carbon accessories such as seatposts and bars.
No worse than metalDave Hickey
Aug 5, 2003 5:58 PM
Put a big gouge in one of todays light weight aluminum seat post or bars and you could have the same result. There was a post earlier this week about someones aluminum bar that failed. It failed without warning. I wouldn't trust a carbon bar with gouge into the fibers but I wouldn't trust an alloy bar big gouge either.
True?.... sort of - you might want to read this.Synchronicity
Aug 5, 2003 11:19 PM
Any scratches will weaken a material, even metals. That is why polished items have a greater fatigue strength.

*BUT* the thing is carbon fibres are only strong because the individual fibres have a very small diameter. That is the only reason a carbon fibre is any stronger than a lump of charcoal. This small diameter reduces the number of imperfections on the microscopic scale. It is that fact that makes them very strong. Aluminium in bulk form, such as a seatpost, is no where near as susceptible to scratches as a fibre-reinforced composite is.

For my degree I did this laboratory experiment where we tested the strength of a *single* carbon fibre! They only take about one newton of force before they break!! It was very hard to set it all up, but I can tell you that if it would have only taken a scratch 1 micron deep in a 6 micron fibre to affect that strength. In comparison, a one micron scratch in a lump of metal is *nothing*. THAT, my friend, is the bottom line.
B.Sc. (Materials Science)
Wait a minute ...pmf1
Aug 6, 2003 10:33 AM
Doesn't carbon fiber derive its strength from being woven together into a cloth and impregnated with resin? Testing a single strand seems about as valid as testing a single tiny strand of a climbing rope and concluding its not strong because it can't withstand a fairly deep incision.

Personally, I think there is so much urban legend regarding carbon bikes. They're just as strong as any other bike. They don't shatter, melt or suddenly crumble from a scratch. This is all from my own personal experiences riding them for the last 10 years so, THAT, my friend, is only my opinion
Ph.D. (Economics)
works stands are padded...C-40
Aug 5, 2003 7:17 PM
My park stand has heavy rubber padding in the clamp area. Putting the post in the work stand isn't nearly as stressful as clamping it in the frame.
re: Work stand and carbon seat postJervis
Aug 5, 2003 1:52 PM
Just clamp it onto the post, but be very careful about the pressure you use, as said above. I used to work in a shop and made the mistake of clamping a new bike via the seat tube and it wrinkled the crap out of the decal.

Jervis
use a shop rag and don't clamp too tightmaurizio
Aug 6, 2003 9:10 AM
Just clamp it to your post. Wrap the post with a shop rag first and don't excessively tighten the clamp on the post and you'll be fine.
The rag will prevent scratches and act as an extra buffer with your post.
I wouldn't switch to an aluminum post - especially - if you are doing this often as this is going to stress out your frame and seat post clamp as well as give you a hassle tring to align your seat to the where it was before.