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I have a carbon fork, and a crown race that fits a sealed cartridge headset bearing. I know that in installation of crown races on metal steerer tubes, the use of grease is recommended.

I am wondering if a similar/alternative material is available/recommended when the steerer material is carbon fiber? Or is the crown race supposed to go dry onto carbon?

I have some concerns about the health of the CF over a prolonged period of time if grease is applied, but I have no data to back up these concerns.

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  • Since you're using cartridge bearings, which incorporate the bearing race within it's structure, the crown race of the fork steer tube is essentially only a bearing seat. No balls will interface with it. As such, one can use a split crown race. Simply the correct size crown race with one cut in the circumference. You can do it yourself to your current one with a hacksaw or rotary tool. The installation will then be tool free but it won't be loose either. The race should be installed with the split to one side not to the front or back. This is the way to go with a carbon steerer.
    – Jeff
    Jun 26, 2023 at 18:03
  • You'll still want to find some quality carbon fiber compatible grease to use. One, to prevent galvanic corrosion, and two, the bearing--race interface should be greased and that will get on the steerer tube.
    – Jeff
    Jun 26, 2023 at 18:06
  • The crown race is already slotted, but it appears to be too narrow, so it stretches a bit much, and it doesn't sit perfectly well with the bottom headset bearing. But this is a different problem (that I may be able to live with). The important thing I wanted to address is that @Paweł's answer does not mention anything about CF-specific greases. If you have any data to back up this claim of "carbon fiber compatible grease", you would be more than welcome to share it in a proper answer.
    – jayded-bee
    Jun 26, 2023 at 21:45
  • Regarding the poor seating of the already split crown race: is it certain that the steerer tube doesn't have an integrated crown race? It'd be part of the tube structure and the taper of the steerer tube may cause one to not notice it if it's not expected. Just a thought. Not trying to insult your intelligence, rather it comes from realizing that would be something I would do
    – Jeff
    Jun 27, 2023 at 5:13
  • @Jeff I think the reason it doesn't fit well is that it's a project with random components I could find online. It's a cheap carbon fork from China. ("95 mm instead of 100 mm spacing" type of cheap.) 1" steerer, because it's going to be paired with an old steel frame. The headset cups and bearings and crown race are all random acquisitions with no guarantees that they will fit. I don't have a workshop (nevermind a lathe!) so I'm limited to finding sellers who cater to the demographic that upgrades 40 year old frames.
    – jayded-bee
    Jun 27, 2023 at 8:59

1 Answer 1

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What is commonly called carbon fiber should actually be referred to as carbon fiber-reinforced plastic, or CFRP. It consists of carbon fibers in a matrix.

In the cycling industry, the matrix is usually made of thermoset resins, which consist of very large molecules with a very high degree of covalent bond cross linking. This structure is created during the curing process, which leaves the cured resin resistant to many chemical agents, including oils, soaps, fatty acids, and low concentration acids - basically main ingredients of modern greases.

The graphite itself is also rather non-reactive and will resist commercial-grade greases.

For completeness, one should also mention the interface between the fibers and the matrix, which is a mixture of hydrogen and covalent bonds. However, this interface is usually not exposed to the outside world due to the manufacturing process, and even if it was, it is still a tough barrier for most chemicals to traverse.

You can find compatibility charts for different types of CFRPs and resins, such as this one or this one.

That being said, manufacturers do suggest to use grease when interfacing metal and carbon (e.g. here), also to avoid galvanic corrosion. And honestly, I would be much more concerned with that than chemical reactivity of grease.

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  • I am aware of grease being applied to metal steerers due mainly to galvanic corrosion. However, I don't see how this could happen when the material is not conductive, such as with a CF steerer? (CF here being shorthand for fiber weave drenched in resin.)
    – jayded-bee
    Jun 26, 2023 at 12:22
  • @jayded-bee: carbon is very much condictive, therefore CFRP can galvanically corrode if the fibers come in contact with a metal, see this for instance: corrosionpedia.com/…
    – Paweł
    Jun 26, 2023 at 12:28
  • carbon, yes, but as we've established it's all covered with copious amounts of resin. Note taken that there is a possibility to damage the surface of the steerer to the point to where actual carbon fibers are exposed. Thanks for the points made, cheers!
    – jayded-bee
    Jun 26, 2023 at 12:33

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