A Forgotten Seat Post Installation Secret (or at least it seems that way)

From Rookie’s Keyboard

Hello, friends

Yesterday I went to the LBS (local bike shop) to get a new rim tape for my road bike. And while I was waiting for the guy there to find the size that I needed I had the opportunity to observe the mechanic in the shop who unfortunately appeared a little depressed for whatever reason.

Psychology aside, I saw him install a completely new seat post on an old bike without putting grease on it. To the untrained eye, this may seem like an ok practice, but it actually isn’t. And no, I am not picking on the guy. In fact, I am thankful that he inspired me to write this post.

Naturally, many rookies out there consider seat posts a “set it and forget it” component. It makes sense. After all, seat posts don’t move. Why would they need cleaning and lubrication?

The truth, dear rookies, is that a neglected seat post could lead to a seriously unpleasant situation.

Without lubrication, the seat post could corrode to the point of no return. There are plenty of videos online of people using all kinds of contraptions as well as chemicals to remove a seized seat post. Some even resort to cutting it out of the frame with a sabre saw.

The drama could be avoided, if you apply a thin layer of grease on the seat post.

Seat Posts and Corrosion

A chemical reaction known as reduction-oxidation or redox can cause corrosion of the seat post.

redox reaction consists of two simultaneous processes known as oxidation and reduction.

During oxidation an element, in this case, metal, loses an electron.

During reduction an element, in this case, oxygen, gains an electron.

The reduction process stimulates the formation of negative oxygen ions as a result of the extra electrons (electrons have a negative electric charge).

Water and heavy moisture “encourage” the redox reaction by acting as an electrolyte solution facilitating the transfer of ions between two elements.

When the negative oxygen ions penetrate the metal, they stimulate the formation of a new “oxide” surface.

The most basic example would be the rust found on iron objects exposed to humidity.

For the same reason, seat posts made of steel rust after prolonged exposure to the elements.

The formed rust binds the seat post to the seat tube and if left untreaded the seizure could reach EPIC proportions. In the worst scenario, the entire frame is totaled.

When an old frame is sold with a seat post in it, there’s a 99% chance that the seat post is seized.

Basic Grease = Seat Post Savior

A thin coat of basic grease forms a protective film isolating the seat post from the environment and eliminates the chances of metal oxidation.

Why grease instead of other lubricants?

  • Higher viscosity

Grease is a semi-liquid and has a long lifespan. Unlike other lubricants, its molecules experience higher friction when moving, and the flow is slow.

Liquid oil has protective qualities too, but its low viscosity makes it a poor choice as a seat post-lubricant because the parts are vertical. That said, oil is still better than nothing. It just won’t last.

Aluminum Seat Post Can Be Problematic Too

Aluminum is a lot more resistant to the elements and doesn’t rust.

However, an aluminum post needs lubrication too. When aluminum is exposed to air, it forms a protective upper layer known as aluminum oxideIt is precisely this layer that protects aluminum against further corrosion.

If the seat post isn’t treated, the aluminum oxide layer will bind to the frame.

And if the frame is made of steel, the problem will be pretty bad due to the phenomenon known as galvanic corrosion (remember that term as it’s been the source of a lot of anger). 

Galvanic corrosion occurs when two dissimilar metals (steel and aluminum in this case) are in contact with one another in the presence of a conductor like water.

Aluminum starts losing electrons even though it’s more corrosion-resistant than steel. This is a custom scenario known as preferential corrosion.

Once the aluminum is corroded, it forms a very strong union with the inner parts of the steel seat tube, and it becomes super difficult to separate the two.

Of course, the process takes time. If you periodically remove the seat post (e.g., every 3 months) and grease/re-grease it, the corrosion will be prevented.

A Word On Carbon Seat Posts

Somewhat unsurprisingly, carbon demands a different approach than metal. 

For the following reasons, it’s not recommended to use grease on a carbon seat post:

  • Amplified clamping pressure

Grease decreases the friction between the seat post and the seat tube. Consequently, to keep the seat post in place, the clamp will have to be tightened harder.

Carbon doesn’t deal well with compression (unlike metal) as it can easily be crushed.

The solution?

Carbon assembly compound/paste. This is a special lubricant made specifically for carbon elements. It has the following crucial properties:

Increased friction. The carbon paste increases the friction between the seat post and the seat tube (the opposite of what grease does). As a result, less clamping pressure is required to keep the seat post at the needed height.

The lower clamping force minimizes the chances of crushing the seat post.

  • Prevention of corrosive reactions

The carbon assembly compound acts as a sealer.

Carbon Can Experience Galvanic Corrosion Too

Carbon acts as an electrical conductor. Consequently, if you combine an aluminum seat post and a carbon frame, galvanic corrosion is once again a possibility.

To avoid this issue, some carbon frames have an aluminum sleeve in the seat tube. The goal is to prevent contact between two dissimilar materials (carbon and aluminum in this case). When you have aluminum on aluminum, the chance of having your seat post stuck is much lower.

If you have a carbon frame, another option to prevent corrosion would be to get a carbon seat post too.

I know that at this point most rookies reading this are already on their way to the local hardware store to buy grease…and some are probably wondering what type to get.

Simple answer – everything will work (unless you have carbon as explained above).

Longer answer:

The seat post doesn’t move or heat up because of friction. As a result, it doesn’t require high-end grease. If the seat post and frame are made of aluminum or steel, you can use general-purpose grease. That’s what I use.

Some people think that lithium grease can harm aluminum, but this is doubtful because the lithium in the grease has lower reactivity.

If you live in a rainy, coastal area and want extra protection, you could consider using marine grease, which is a special type of grease (blue in color) that provides rust and corrosion protection in both freshwater and saltwater environments.

And now you know why I wasn’t happy to see the mechanic in that shop re-install the seat post without applying grease. The seat post looked to be made of aluminum whereas the frame was from an old 26-er MTB. (A nice bike otherwise).

But thankfully, this is a fairly simple procedure that we can do ourselves regardless of skill level. If you have a quick-release seat collar you won’t even need a key to remove the seat post.

And since this turned out to be a fairly long post, I will include a TL: DR;

  • Seat posts can seize into a frame when the two are made of dissimilar materials (e.g., Aluminum and steel).
  • To prevent a stuck seat post, apply a light coat of grease on it every 2-4 months.
  • If you have a carbon seat post, DO NOT use grease. Instead, get carbon compound paste. It increases friction (thus no need to overclamp things) and protects the unit from the elements.

Until next time.

– Rookie






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