Seatpost Maximum Insertion?
 

Hey all, I purchased a new seatpost for my bike. It's 350mm in length and I'm finding my comfortable ride height to have the post over 200mm into the seat tube. Is this okay to be in so far or should I cut the seatpost to a shorter length of say 250mm?

Thanks

I have not heard of maximum insertion, but there is a minimum insertion so don't cut it too short.

It's okay.

Having more post inserted means there's more to get stuck. If you do cut it, it's a good idea to mark a new min-insertion line.

Just move it once in awhile so it doesn't get stuck and it will be fine. I did have one hit the bottle cage bolts so I had to switch to a shorter post which was a bit odd considering the frames I ride.

cut it. what's the point of burying unnecessary aluminum in the seat tube? might as well fill it with cement.

I just want to be sure its safe from a structural standpoint. I have greased the inside of the seat tube and not worried about the extra weight as the post is very light.

Cut one out once, and you will never have a seat post inserted this far ever again.

Just curious what causes them to get stuck? I can see it happening with a steel post in a steel frame but how about alloy in a steel frame? This bike had an alloy seat post from the mid 70's that slid out like butter.

I have seen one stuck for mechanical reasons, probably hammered in, and all others were corrosion (aluminum oxide, rusting steel, etc). Aluminum is an active metal and untreated (not greased) will corrode in a New york minute. Your friend is anti-sieze lubricant, apply once and forget about it.

This:

Galvanic corrosion - Wikipedia, the free encyclopedia

Thanks for the science lesson there lol. Anyway, I liberally applied grease and have the seatpost well in there. I am a bit apprehensive to cut it but we'll see. As long as it cannot cause any other structural issues I am fine with it as is.

Thanks all! Great forum!

You hit the water bottle boss on the seat tube. thats the limiting factor ..

make it a point to remove and re grease the seat post every few years..

I don't see any point in cutting it. As long as you keep a barrier between the aluminum and steel to prevent corrosion, you should be fine.

But it brings to mind an interesting, if possibly meaningless, question. Say the frame is double butted 531 or similar. How far down the seat tube does the butted section of the tube extend? If the extra long seat post protrudes down into the un-butted, larger diameter section of the tube, are there any implications with regard to leverage, lack of contact with the steel, etc.? Probably not. I'm just letting my fetid imagination wander, as usual.

[MENTION=29368]rootboy[/MENTION] - your feted imagination wandering around in the seat tube with a seat post cause me to respond with the following observation. There might be an opportunity for an untreated post to corrode in the gap making the post larger in diameter than the ID of the butted section. Result may be a loose post but not removable due to the corroded OD being larger than the butted ID.

I've wondered about having too long of a seatpost sticking out of the frame (even if withing the minimum insertion) creating a lever underneath my hefty weight if I sway too much from side to side leading to torquing on the seat tube, but hadn't considered the opposite.

Kestrel considered that when bikes that tipped over broke the seat tube.

So far I haven't had an overly stuck seat post. The Colnago Seatpost has had mighty few adjustments over the last 30+ years.

Personally, I'd leave it uncut. The next person might want it longer, or perhaps you'll loan the bike out sometime. Or, maybe tinker with the pedals, cranks, or other adjustments that would affect the seat height.

The more post, the less torque on the end of the seat tube & clamp.

Some MTBs have mighty long seat posts.