Condensed answer: A carbon seat post can be installed in a steel frame but has to be covered in a thin layer of carbon assembly paste.
The carbon assembly paste serves two purposes – it increases the friction between the seat post and the seat tube while also protecting the parts from corrosion.
Can a Carbon Seat Post Get Seized In a Steel Frame?
Yes. A carbon seat post can get stuck in a steel frame for two reasons:
Steel frames are susceptible to rust. If water gets into the frame for a prolonged period of time, the insides of the frame could rust. As a result, the effective diameter of the seat tube will get smaller, and the frame will grab the seat post.
Galvanic corrosion is a deterioration process occurring when two dissimilar metals are in contact and in the presence of a conductor like water.
Carbon composite isn’t a metal, but it’s highly conductive and leads to galvanic corrosion too.
When the above conditions are met, a transfer of electrons begins from one of the materials to the other.
Galvanic corrosion is a lot more likely to occur when using plain steel which is the type that most steel bikes are made of.
Stainless steel is a lot less susceptible to galvanic corrosion, but it’s not the preferred material for bike frames. If you have a steel bike, chances are that it’s made of regular non-stainless steel for the following reasons:
- Stainless steel is expensive to the point where many people would simply buy a titanium frame.
- Many frame builders refuse to work with stainless steel because the process is too complicated.
- If taken care of, regular steel lasts forever anyway.
But even if your frame is made of stainless steel, it’s still susceptible to pitting and crevice corrosion.
If galvanic corrosion takes place, it will become ridiculously hard, if not impossible, to remove the seat post without damaging it beyond repair.
For that reason, it’s of utmost importance to stop the exchange of electrons between the steel frame and the carbon seat post.
The two most effective ways to prevent galvanic corrosion are:
1. Electrically isolating the two parts to stop the flow of electrons between them.
2. Limiting the moisture between the elements.
If you wrap the seat post in a material that doesn’t conduct electricity, galvanic corrosion will not occur.
This solution is not the most convenient because the seat post’s thickness will increase and prevent it from fitting inside the frame.
Also, some isolating materials could make the seat post extra slippery. As a result, the seat post will keep sinking into the frame.
Hence why the most common method to prevent galvanic corrosion is to apply some lubricating paste on the seat post.
Grease or Carbon Assembly Paste?
Regular grease works just fine when the seat post and the frame are made of metal. However, in the case of carbon one could face a problematic situation when relying on grease to prevent corrosion.
- Seat Post Slippage
Grease makes components slippery. To prevent the seat post from slipping, the natural reaction is to simply tighten the clamp.
This may not be a problem with metal parts, but carbon doesn’t like being squeezed because it has poor resistance to clamping force/compression and can crack.
For that reason, one has to use a torque wrench when tightening the clamp of a carbon seat post. The torque wrench ensures that the squeezing force stays within the specification of the manufacturer.
The increased slippage and the subsequent extra clamping force make grease a less desirable solution.
Below you will also find quotes from manufacturers in regards to using grease on carbon:
No grease on carbon posts. Grease contains certain minerals that can attack clear coats, can penetrate the resin matrix and could cause swelling of the composite laminate. Can you say “stuck seat post?” Don’t use grease.
John G. Harrington
Vice president, bicycle products
Easton Sports, Inc.
No grease. In some cases it can be dangerous to use grease as the chemical composition can cause a reaction between materials. Besides, it increases the torque required to clamp the post.
Ultimately, it’s better to use carbon assembly paste instead of grease. The carbon assembly paste has two functions – it repels moisture and increases the friction between the seat post and the frame.
As a result, the seat post collar doesn’t have to be overtightened to keep the seat post in place.
FAQ: What Will Happen If I Don’t Apply Anything on the Seat Post?
Some people seem to experience no problems if they run the seat post dry for a while.
In the long term, however, the seat post is likely to seize unless you remove and clean it regularly.
FAQ: My Seat Post Is Completely Stuck. What now?
One way to facilitate the removal of the seat post would be to heat the seat tube with a heat gun. The goal is to expand the seat tube by raising its temperature.
When that happens, it may be possible to remove the seat post without applying destructive force. If a heat gun isn’t available, one can also use a hairdryer or pour hot water on the seat tube.
Note: Heat methods damage the paint because it’s not resistant to high temperatures.
If the situation is helpless, the only option is to destroy the seat post. This could be done by making multiple cuts across its length and then pry it out piece by piece with a flat hat screwdriver.
Once the seat post is out, gently sand the inner walls of the seat tube.
Summary: What You Need To Know
1. A carbon seat post can be installed in a steel frame as long as it’s covered in a thin layer of carbon assembly paste.
2. The carbon assembly paste repels moisture and reduces the clamping force needed to hold the seat post in place. The result is reduced stress on the carbon walls.
3. Grease is not the best choice because it increases the chances of a slipping seat post and incentivizes the user to tighten the seat post collar more.
4. Treating the inner parts of the frame against rust is also beneficial.