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Old 03-26-08, 07:40 PM   #1
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Aluminum Seatpost in a Carbon frame

Is it okay to use a little film of Park Tool grease on a Thomson aluminum seatpost before inserting same into a carbon fiber bike frame?

If not, what can I use to forestall galvanic corrosion.

Thanks for all responses.
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Old 03-26-08, 08:34 PM   #2
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can't answer your question directly, but I have on older Kestrel 200si with DA seatpost......been in there for years now, no problems with corrosion. Of course you mileage may vary......
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Old 03-26-08, 09:17 PM   #3
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Nope. You don't lube a carbon post in an aluminum frame, so you don't lube an alloy post in a carbon frame. There are some carbon specific things to provide more grip, but not lubrication. As long as the post is in the frame, you shouldn't have to worry about it corroding.
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Old 03-26-08, 09:40 PM   #4
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I would use some sort of carbon prep. Finish Line makes a good one in a convenient screw top squeeze bottle. I've seen two carbon posts seize in a frame. One was aluminum and one was carbon. Seems like the clear coat on the seatpost comes off and bonds to the seattube. It happened to my boss' Six13 and we had the seatpost head clamped in a vice and we were twisting the frame to get it out. The second was a Bontrager carbon SP and a trek carbon bike. It did not seize completely but it did look like the clear was breaking off and bonding to the inside wall of the seattube
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Old 03-26-08, 09:46 PM   #5
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Idealy, you would have a carbon seat post, to prevent galvanic corrosion. In your situation, the aluminum will corrode because it is the anode with a potential of -1.67, and the carbon the cathode with a potential of +0.81. A difference in potential of 2.48 volts. Where as titanium and carbon both have + potential, and the resulting difference is only 0.755 volts, which is negligible. (Remember kids, that even though both carbon and titanium are both + charges, its the difference in potential that creates a charge.

To reduce or prevent the effects of galvanic corrosion, you can simply get the aluminum seat post anodized, which would give it a non-conductive coat to it. Or a very fine rubber wrap would do just as well.

Don't be fooled by the black color, or that carbon isn't a metal. Carbon is highly conductive.
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Old 03-26-08, 10:00 PM   #6
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Idealy, you would have a carbon seat post, to prevent galvanic corrosion. In your situation, the aluminum will corrode because it is the anode with a potential of -1.67, and the carbon the cathode with a potential of +0.81. A difference in potential of 2.48 volts. Where as titanium and carbon both have + potential, and the resulting difference is only 0.755 volts, which is negligible. (Remember kids, that even though both carbon and titanium are both + charges, its the difference in potential that creates a charge.

To reduce or prevent the effects of galvanic corrosion, you can simply get the aluminum seat post anodized, which would give it a non-conductive coat to it. Or a very fine rubber wrap would do just as well.

Don't be fooled by the black color, or that carbon isn't a metal. Carbon is highly conductive.
The Thomson seatposts are already anodized I think. Are they not?
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Old 03-26-08, 10:04 PM   #7
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General recommendation would be run a light coating of carbon assembly compound to prevent slippage which is a more routine occurence than corrosion. Finish line, Tacx, and others make it. If you don't have that handy, forgo the use of grease and just properly torque the binder bolt......if you notice slippage, order the aforementioned compound.
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Old 03-27-08, 02:50 PM   #8
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The Thomson seatposts are already anodized I think. Are they not?
Mine seems to be. I've had a Thomson in a CF frame to 4 years with no signs of any corrosion, electric or chemical.

Al
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Old 03-27-08, 03:15 PM   #9
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Some carbon frames have an aluminum insert bonded into the seat tube. If this is the case with your frame, then it's aluminum on aluminum, so grease away. You may have to remove the seat post clamp to determine if it has an insert.
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Old 03-27-08, 09:13 PM   #10
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Originally Posted by JoeBoxer View Post
Idealy, you would have a carbon seat post, to prevent galvanic corrosion. In your situation, the aluminum will corrode because it is the anode with a potential of -1.67, and the carbon the cathode with a potential of +0.81. A difference in potential of 2.48 volts. Where as titanium and carbon both have + potential, and the resulting difference is only 0.755 volts, which is negligible. (Remember kids, that even though both carbon and titanium are both + charges, its the difference in potential that creates a charge.

To reduce or prevent the effects of galvanic corrosion, you can simply get the aluminum seat post anodized, which would give it a non-conductive coat to it. Or a very fine rubber wrap would do just as well.

Don't be fooled by the black color, or that carbon isn't a metal. Carbon is highly conductive.
Everybody that does not believe you need to grease carbon posts in an Al frame, or vice versa, should read JoeBoxer's posting repeatedly until they understand the reality of what's going on. Carbon fiber IS conductive and any CF/AL interface IS subject to galvanic reaction. And, it WILL corrode if not treated properly (i.e. grease it).

Don't believe this??? Get a nice CF frame and Al seatpost and get some sweat dripped down in there (i.e. just like it happens on many bikes used on trainers all winter). Or, drive the bike down by the seashore. Then just wait a few months and try to remove the seatpost. Best luck with that. I've now been witness to two totally ruined CF frames and there is plenty of additional anecdotal evidence to support the reality of galvanic reactions.

That nonsense about "don't grease any CF" has been debunked about a zillion times now, even by CF manufacturers themselves.

Dissimilar metals will react and corrode and eventually bind in some very inconvienient modes.
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Old 03-28-08, 03:04 PM   #11
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I still hold to my above answer and check this link out from Leonard Zinn with responses from Easton, Bontrager, etc. on why they DO NOT recommend grease on CF components. http://www.velonews.com/article/8835

The issue of greasing CF has not been debunked by manufacturers as they still encounter slippage issues hence why many bars & stems are shipped with textured areas. Also, very install fact sheet for CF components that I have ever seen also specifically states not to use lube.
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Old 03-28-08, 07:34 PM   #12
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I still hold to my above answer and check this link out from Leonard Zinn with responses from Easton, Bontrager, etc. on why they DO NOT recommend grease on CF components. http://www.velonews.com/article/8835

The issue of greasing CF has not been debunked by manufacturers as they still encounter slippage issues hence why many bars & stems are shipped with textured areas. Also, very install fact sheet for CF components that I have ever seen also specifically states not to use lube.
We are not talking about "bars & stems". This discussion is about seatposts. Anybody stupid enough to grease a stem/bar interface deserves what he/she gets. Common sense dictates you DON'T do that. Seatposts, on the other hand, are totally different. The stem/bar interface does not typically get totally frozen/welded together. On the other hand, the seatpost/frame interface presents a much different problem. And, if you get it wrong, you toast a frame.

For the umptieth time, read this discussion:

http://www.velonews.com/article/9023

Craig Calfee, CF guru, knows what he's talking about. Even note that he states that anodizing just slows down the galvanic reaction. It does not prevent it.
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Old 03-28-08, 07:46 PM   #13
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Rofl cascade for the pwnage. K thx bai.
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Old 03-28-08, 08:19 PM   #14
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Rofl cascade for the pwnage. K thx bai.
I think it was Raiyn (BTW, good to see you around again) that used to get on the users about using "AOLese". Thanks for illustrating his point.

I apoligize to all, about making comments that are off topic. Something that others would do well to respect.

Let's stick to the technical discussions and respect oposing opinions. I know that some people and manufacturers state, explicitly, that you don't grease CF. But, experience shows that, if you don't, you may give up a frame due to a permenant bond between the CF frame and Al seatpost. Owners of CF framed bikes can judge for themselves.

Maybe I missed it, but I have not yet seen a post where someone declares that greasing their CF seatpost has damaged their bike. To paraphrase the late, great, Sheldon Brown, "if it slips, don't grease it ..., if it does not, then grease it". A lot of this is just common sense, but to state that one method, or the other, is absolute, is just silly. My point is that I have alway greased CF/Al interfaces and never had a related problem. I've never had a customer complain of slippage. In the case of a CF seatpost and an Al frame, I always hone the seattube and grease the frame. I always hone Al seattube frames to make sure that the seatposts don't get scratched. Seattube hones and the appropriate lube are expenses well spent.

It ain't rocket science, but if you don't accept the concept of galvanic reactions, then you really don't want to understand what's really going on.
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Old 03-29-08, 09:17 AM   #15
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Touche Mr. Cascade.

I respect your opinion and experience on greasing and the bit from Craig Calfee is very cool as I had not seen that piece before.

My experience both personal (Trek 5900 OCLV, Cannondale CAAD 5, CAAD 9) and professional is what has lead me to my "general recommendation" aforementioned in the thread. I have seen issues where certain types of grease may have lead to frame issues (namely Lithium based) as a new customer came in about 2-3 years ago and had what I would call a "softening" of the seatube and it had in fact been greased with a lithium based grease. While that generally isn't a cycling grease and the manufacturer and I still debate whether the grease, production defect, other enviromental factor may have lead to the degradation of the tube...in reality we may never know.


My use of assembly compund in many ways offers a similar protection between the CF component and frame material. At least in my experience, never had a customer or my own post stick when using this practice.

I mentioned the texturation of stem & handlebars as anecdotal evidence of slippage issues. Yes, we are talking about seatposts but I have recently seen a few manufacturers "texturing" the surface of their seatposts as well.

I will think long and hard though when/ if I run out of assembly paste as to whether forgo it on a build or just use some grease.

Thanks for keeping me on my toes...

Chris
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Old 03-29-08, 10:26 AM   #16
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How can the CFRP cause any corrosion? Everything that comes in contact with the metal is resin - a plastic. The carbon fibres are never exposed at the surface.
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Old 03-29-08, 11:18 AM   #17
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CDCF,
Check out this article from Velonews and do a search there as well concerning the issues. I think Cascade and I have ridden the wheels off this topic.

http://www.cyclingnews.com/tech.php?...006/news/10-25
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Old 03-29-08, 11:55 AM   #18
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CDCF,
Check out this article from Velonews and do a search there as well concerning the issues. I think Cascade and I have ridden the wheels off this topic.

http://www.cyclingnews.com/tech.php?...006/news/10-25
Ah, I should've been more specific in my previous post. I was referring to galvanic corrosion, of course!
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Old 03-29-08, 07:45 PM   #19
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Te Carbon prep like finish line or tacx will help things not to get stuck but the main benefit is the grit that is in it so that you dont have to over torque the clamps and risk possible crushing of the carbon components.
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Old 03-30-08, 08:08 AM   #20
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Does the frame have an aluminum seat post insert or not? This discussion is silly without all the information.
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