RCMoeur 

I'll just say that when I had creaking noises from a seatpost, it presaged the snapping of the bolt on the saddle clamp from fatigue.

Duragrouch

Excellent point! The bolt had partially cracked through, which reduced stiffness and clamp force, allowing more movement, and squeak. Good warning sign for anything on the bike.

Ron Damon

This is a very strange logic as it would be highly improbable statistically that you had several faulty bikes. A more careful consideration of the issue would focus on the common element to all these allegedly faulty bicycles, to a more statistically plausible cause. That common element is you.

Duragrouch

I just checked engineering tables for static coefficients of friction.

Dry aluminum against aluminum, 1.05

Dry aluminum on mild steel, 0.61

Dry Mild steel on mild steel, 0.74

"Greasy", all of the above, 0.005 (various heavy greases) to 0.23 (light mineral oil)

(By the way, dry aluminum on dry aluminum, sliding (kinetic friction) actually increases, 1.4, (most solid materials, sliding friction is less than static friction); this increase may indicate galling).

So my friends... there may be sufficient friction force on a clamped greased seatpost to hold the rider weight, but it's gonna be a whole lot less than dry.

Now, based on the above, it would be nice to find an online calculator to kick out the total axial friction force, as a function of clamp force, which is a function of the screw force or clamp lever, for dry and lubed. Some assumptions will need to be made, such as:
- Effective clamped axial length; For my clamping collar, I would assume between 1-1.5X its axial length
- Linear relationship between unit clamp force and coefficient of friction, most specifically, that clamp force does not squeeze grease out of contact point sufficiently to increase friction.

Ron Damon

Or we, you could just go with standard practice and ample user testimony. We are not lying or trying to deceive.

Duragrouch

I get that. If everyone is saying it's standard practice to grease the post, and there's not widespread slipping of them, there must be enough friction force. I'm just wondering how much margin there is greased. Because the difference between dry and greased is almost an order of magnitude.

I also do wonder about that part, a greased surface under pressure, whether at a micro level, the grease is being squeezed out, and also the same for anti-seize, because it's like grease but with very fine metal particles that probably stay put; just because I'm curious.

Ron Damon

Bingo!

Duragrouch

I think moreso with your ribbed post. But that's just a pure guess.

grumpus

Back in the day when most bikes had chromed steel seatposts in steel frames we could have problems with them slipping, which was perhaps as much to do with manufacturing tolerances as material choice, but it was OK to drill a small hole in the back of the seatpost and fit a screw to act as a stop. With aluminium posts this is not such a good idea, but fortunately also a far less common problem. The greater problem with aluminium in steel is galvanic corrosion leading to stuck seatposts, which is why greasing is important. Less of a problem with aluminium in aluminium, although different alloys will still have some potential difference, but as you suggested galling might be a problem.

RCMoeur 

Best done after you're 100% certain you have set the fit and height correctly.

grumpus

You can drill multiple holes in a helical pattern to allow fine adjustment, then transfer the height to a 'good" seatpost if you don't like the ventilated one.

smd4

I prefer not to drill any holes in my bike.

I swear, the hacks you guys come up with…

Kontact

You're going to seize your post in place by not greasing it. That's basic bike mechanics.

Kontact

As seen in multiple threads, you have some weird ideas about lubricants - and many of them are wrong. Maybe stop offering advice about them?


And anyone drilling a hole right about the seat tube clamp on their seatpost is asking for a broken seatpost. That's the stress riser.

sweeks

Hasn't happened in over 20 years. Seems like waiting for the Rapture.

But, seriously, the post on a folder like mine is huge, both in length and diameter, by comparison to those on regular bikes. Mine, and thousands like it, work fine without lubrication.
All my other bikes with normal seatposts (AL in AL frame, Steel in steel frame, Ti in Ti frame) are well-greased.

Kontact

The OPs bike is not a folder, so maybe advice that is intended for folders isn't applicable to this thread?

sweeks

Good point. But there's been a fair amount of folder chat included. I think anyone who's following the thread won't be confused.

bboy314

Yeah, I don’t know how this turned into a folding bike thread, but hopefully the very basic and important concept of greasing metal seatposts on traditional bikes is not lost on anyone reading it.

grumpus

Do you have a steel seatpost in a 1960s bike? Because that's what I was discussing - maybe you missed the context.

Kontact

Most bikes ever made are steel bikes with steel seatposts. No new techniques needed.

grumpus

Definitely to be avoided with aluminium seatposts, but an old steel seatpost won't crack in the same way, and it was the custom to have taller frames & shorter seatposts back then so a smaller moment at the clamp/hole too.

smd4

Sorry—that doesn’t change my opinion about drilling holes in bikes.

grumpus

A lot of those bikes are also pretty shoddy, and a slowly sinking seatpost is not uncommon, adding a screw to stop this is not a new technique.

Camilo

No, not confused. But wondering why we're sifting through so much irrelevant discussion. Yeah, I know, it's the internet and digressions occur. I don't know wtf (why tf) it even came up and why it has been so prolonged. It has nothing to do with the OP, nothing,

Duragrouch

Respectfully, I have many weird *questions* about lubricants, when I don't have the answer, and am always open to those that know more about a subject (I think I recognized your knowledge in a very recent other thread). I think my comments above were asking just such a question. Because the book says greased static friction is very low, but greased posts seem to hold. However I have not yet done the calculation on clamping force for what it's supposed to be, so it's still up in the air for me.