Read This Before Throwing Your Carbon Post In an Alloy Frame 

from Rookie’s keyboard

Hello, friends 

Here’s an important tip:

Before installing a carbon seat post in an alloy frame, apply a thin film of carbon assembly paste on the seat post to increase friction (reduce clamping requirements) and eliminate the chance of galvanic corrosion. 

Otherwise, the carbon seat post may get stuck in the frame, and the seat collar may have to be tightened beyond the recommendations due to the lack of friction against the seat tube.

Aluminum Corrosion

Unlike steel, aluminum doesn’t rust. When exposed to the elements, aluminum experiences oxidation forming a thin top layer known as aluminum oxide.

The layer shields the underlying aluminum and protects it from further corrosion. If the protective oxide film is damaged, it regenerates quickly in the presence of oxygen. Hence why aluminum is known to resist deep corrosion better than iron.

The corrosion reduces the seat tube’s diameter and could result in a seized seat post. Once stuck, the carbon seat post becomes very difficult to remove.

Galvanic Corrosion

Aluminum alloy is prone to galvanic corrosion when it’s in contact with carbon composite.

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.

The aluminum frame is acting as an anode giving up electrons whereas the carbon seat post is a cathode receiving electrons.

Galvanic corrosion between aluminum and carbon

After the occurrence of galvanic corrosion, the seat post becomes almost permanently stuck into the frame.

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 something 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.

The most common method to prevent galvanic corrosion is to apply some lubricating paste on the seat post.

What Substance To Use 

Manufacturers of carbon seat posts recommend applying a thin layer of carbon assembly paste before installation.

The paste has two functions:

  • Repel moisture
  • Increase friction between the seat post and the seat tube

The extra friction reduces the clamping force needed to hold the seat post in place. As a consequence, the clamp doesn’t have to be tightened significantly. 

This is beneficial because carbon has poor resistance to compression and can be easily “crushed”.

Regular Servicing = Ideal

A carbon seat post may get stuck in an aluminum frame even when carbon paste is applied.

The chances are extremely low, but the outcome is not unheard of when the seat post hasn’t been removed over a long period.

It’s recommended to gently clean the seat post and re-lubricate it at least a few times a year.

Grease = No

Don’t apply grease on a carbon seat post for two reasons:

  • Grease can soften the outer coat and cause swelling of the composite laminate. Subsequently, the carbon seat post expands and seizes into the seat tube.
  • Grease lowers the friction and increases the torque needed to hold the seat post in place. 

Until next time, 

– Rookie






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