2

I've been riding with my very short seat post extended well past its maximum extension line for quite a while now. Looking at the seat post itself I don't see any signs of deformation or damage other than some very minor surface rust.

Could my bike frame have been damaged? Could the lever force have damaged the frame? I can post some pictures of the frame if needed. My bike is all aluminum.

  • What materials (carbon, aluminum, or steel) are the seat post and frame made from? – Kibbee Oct 20 '14 at 15:07
  • Bike's all aluminium. – Dissenter Oct 20 '14 at 15:08
  • Definitely, if the post does not extend down roughly 3 inches into the frame then you're at risk of damaging the frame. And this risk is greater on an Al bike than a steel one. – Daniel R Hicks Oct 21 '14 at 0:53
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Pull the post and hold it next to the seat tube to see how far it goes in.

If it does not go in far enough to be into the seat tube below the top tube you are putting a LOT of stress on the top of the seat tube.

Believe that maximum mark on the seat post. A seat post is not that expensive to risk damaging a frame.

This is just one (not cheap) seat post but that min mark is pretty conservative. If you are cheating the min mark you playing with danger.

enter image description here

SeatPost

  • I bought a longer post myself for my bike, 20cm exposed (not sure no the total length), cost $10 at the LBS. – BPugh Oct 20 '14 at 19:12
3

Answer: This is what can happen.

Please check my question at What caused this seat clamp / frame failure? This was caused by a really long seat post installed way too far up.

http://i.stack.imgur.com/1CiVW.jpgenter image description here

I also have a bad habit of bending seat posts at the point they enter the frame, mostly due to the leverage from being so long.

3

Yes, you can damage the frame if the seat post is too short.

I have personally seen someone sit down on an overextended seatpost and fall off the bike as the seat post was wrenched out of the seat tube. The collar went flying and the top of his seat tube was mangled. His frame was titanium and he was able to bend it back. You probably wouldn't be able to salvage it with aluminum.

In all likelihood, the minimum insertion line is at least somewhat higher than it needs to be in (courtesy of the lawyers). My gut tells me that it's fine as long as the seat post extends into the seat tube an inch or two past the top tube and seat stays. However, that is my gut. Don't take it as gospel.

If in any doubt, buy a longer seat post. They're cheap. A frame is expensive.

  • Agreed, not only a frame is expensive, but replacing a frame may mean a lot more additional work compared to replacing a seat post. Effectively, the bike may be "totaled" after breaking the frame. – ttarchala Oct 26 '14 at 22:09

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