Carbon seatpost in a steel frame

plug1n

I need a longer 26.8mm seatpost on a winter bike with >20mm setback

There are not many options, but I'm tempted by a carbon post at http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0202831003 (they tell me it has 27mm setback when flat!)

I'm worried about putting the carbon post in a frame that has always been well greased.

As long as I thoroughly degrease the inside of the seatpost, should it be OK?

Also I managed to snap a binder bolt on this bike, do I need to consider the torque?

Thanks

Clever Pun

the binder broke on mine as well recently (not a carbon)

other than that I've nothing sorry

Monty Dog

Ironically, the carbon post is less likely to corrode and stick like an aluminium one because of the nature of the materials. There have been some concerns about certain types of carbon posts suffering from grease contamination - these tend to be the high-end, bare carbon jobs, whereas most carbon posts have a protective clear lacquer. Provided the seat tube has been cleaned, there's unlikely to be any contamination. There are also plenty of non-petroleum based anti-seize compounds available. May be worth checking that your seat bolt snapping wasn't due to trying to hold a post in a mis-shapen seat tube - over-torqueing is not good for carbon.

dennisn

Make sure you grease the carbon post before puttting it in, otherwise it will cause a sort
of galvanic corrosion with the steel bike and pretty much weld itself in there and never come out. Strange but true. Just because it's carbon fiber doesn't mean it won't react
with some other materials(steel, aluminum, titanium).Some people use some sort of product that is made for this scenerio, but good old grease will work.

dennis noward

redddraggon

dennisn wrote:

Just because it's carbon fiber doesn't mean it won't react
with some other materials(steel, aluminum, titanium).

Carbon Fibre is rather inert, and will not react with those metals.

However the matrix of the composite is a polymer, therefore if used with certain solvents liquid can get into the matrix and make it swell. This swelling is the problem that people may experience if they use the wrong grease.

dennisn

redddraggon wrote:

dennisn wrote:

Just because it's carbon fiber doesn't mean it won't react
with some other materials(steel, aluminum, titanium).

Carbon Fibre is rather inert, and will not react with those metals.

However the matrix of the composite is a polymer, therefore if used with certain solvents liquid can get into the matrix and make it swell. This swelling is the problem that people may experience if they use the wrong grease.

Got to disagree. It is corrosion between carbor fiber and metal. There is a substanstial
difference in the galvanic corrosion potential of carbon and aluminum that causes this
effect. Aluminum / carbon is the worst and titanium /carbon is the best mix as far as bike
materials go. Either can cause problems.

dennis noward

redddraggon

dennisn wrote:

Got to disagree. It is corrosion between carbor fiber and metal. There is a substanstial
difference in the galvanic corrosion potential of carbon and aluminum that causes this
effect. Aluminum / carbon is the worst and titanium /carbon is the best mix as far as bike
materials go. Either can cause problems.

dennis noward

Carbon maybe, but CFRP as a composite no.

Dennis point me towards some academic papers, I can't seem to find any.

I'll have a delve into my textbooks aswell.

redddraggon

All the sources I can find say things along the lines of "impeccable corrosion resistance"

robbarker

Care to point us to a reference Dennis?

dennisn

Try this

http://www.calfeedesign.com/whitepaper8.htm

Item #4 - interfacing carbon with metal parts

Dennis Noward

feel

Not sure where, but i am fairly certain that i have read that you do not need to grease carbon seatposts. Would the considerable layer of lacquer they have on them not isolate them sufficiently to prevent corrosion?

redddraggon

feel wrote:

Not sure where, but i am fairly certain that i have read that you do not need to grease carbon seatposts. Would the considerable layer of lacquer they have on them not isolate them sufficiently to prevent corrosion?

Corrosion isn't problem.

dennisn

feel wrote:

Not sure where, but i am fairly certain that i have read that you do not need to grease carbon seatposts. Would the considerable layer of lacquer they have on them not isolate them sufficiently to prevent corrosion?

Well, to be honest I have heard it both ways. Grease / don't grease. I have also read
many a letter to bike columns talking about frozen carbon seatposts.

Dennis Noward

4candles

i used copperslip on mine in an 853 frame it was in there for 8 years... undid the pinch bolt and out it came uncorroded no probs.. didn't really think about corrision at the time.

4C.

Martin Van Nostrand

Wow. Guys, if you don't know what you're talking about, don't promote misinformation.

1. Galvanic corrosion is a major problem with CF posts in metal frames.
2. Grease does not affect CF
3. Assembly paste should be used with CF posts.

See here for expert reference from Zinn and Calfee:

http://www.velonews.com/tech/report/art ... 023.0.html

From Craig Calfee

Dear Lennard,
Thankfully! An opportunity to dispel the myth that one shouldn't grease a carbon post!

I don't know where the myth started, but carbon composites are not affected by grease. Our advice is simple: If the seatpost fits tight, grease it. If it slips, de-grease it. As has been known for many years, when aluminum and carbon fiber contact each other, galvanic corrosion can start. That is why Calfee uses a fiberglass sleeve as a seat tube shim. Aluminum seat tube (or sleeve) and a carbon post will result in corrosion of the frame and possible seizure of the post within the frame. A carbon sleeve on an aluminum post will result in corrosion of the post. Salty environments accelerate this corrosion. Anodizing merely slows it down. About the only common chemical that will hurt carbon fiber is paint remover (which attacks the resin between the fibers). But there are many solvents that will dull a nice paint job.
Craig Calfee

AlanW

I had Brian Rourke build me a 853 Audax bike last year. Over the Christmas period I was messing about in the garage (as you do?) and for some unknown reason I decided to remove the carbon seat post.

Dont ask me why...... :?:

But the sodding thing was solid, but after a fair amount of twisting , grunting and turning I managed to turn it about 10mm in each direction. Then I decided to gently warm the seat tube with my heat gun, to get it to expand just a few thou. MISTAKE!!!!!!!

Now it is 100% solid and refuses to budge in any direction.

dennisn

BTBR wrote:

I had Brian Rourke build me a 853 Audax bike last year. Over the Christmas period I was messing about in the garage (as you do?) and for some unknown reason I decided to remove the carbon seat post.

Dont ask me why...... :?:

But the sodding thing was solid, but after a fair amount of twisting , grunting and turning I managed to turn it about 10mm in each direction. Then I decided to gently warm the seat tube with my heat gun, to get it to expand just a few thou. MISTAKE!!!!!!!

Now it is 100% solid and refuses to budge in any direction.

Damn. That just sucks

Mark Alexander

I have a carbon post on a steel frame and have no problems

Jajacp

A friend of mine has a carbon post that has completely stuck in an aluminium shim after about 6 months.

Monty Dog

My own experiences of galvanic corrosion of carbon, alumininium and titanium goes back to 1989 and the design and manufacture of artificial limbs, so probably pre-dates 99% of bike manufacturers and others experiences. Carbon and bare aluminium is a very different proposition to steel and titanium. Out of habit, I try and use a seatpost shim made from acetal e.g. USE to eliminate the problem. The likes of Easton expressly mention not to use grease on their seatposts because of the reaction between petroleum products and the epoxy matrix. Many carbon frames also use an aluminium insert for the seatpost which can also cause problems. Best solution is to clean the surfaces and apply a barrier anti-seize, rather than grease. Equally, remove the post regularly, clean and reapply the anti-seize. Most seat post seizures are down to poor maintenance - period. I have seen people 'unpeel' thin-walled steel tubed frames trying to remove a stuck seatpost - go careful of giving it welly.

AlanW

Done it....got the dam thing out at last!! Spent over two hours last night twisting, pulling, swearing, but finally it was freed

Even liberal amounts of WD40 failed to lubricate the lower half of the seatpost.

The main lesson I have learnt however, is leave the seatpost to cool down every so often. When it finally came out it was so hot that it was untouchable! Of course this makes the matter worse because it expands inside the seat post.

The odd thing is, after cleaning the seatpost and reinserting it into the seattube, it is not even a tight fit. In fact, unless the pinchbolt is tightened up a small amount the seatpost slides down the tube. :shock:

So how did it sieze so solid then. :?:

Never the less, a coating of anti-sieze compound and we are now back up and running.