I know that my bike has a 25.4 mm diameter seat post. So can I purchase any old 25.4 mm diameter seat post from eBay and expect it work with my existing bike seat? Here are some pictures of my existing seat post.

It appears that my bike seat has a little part that slips over the seat post .... I'm assuming that all I need to do is loosen the hex nuts on either side and the bike seat will let go of the old seat post and in the new one goes, right?

ETA: will this seat post work? Thinking of pulling the trigger on this one.


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1 Answer 1


Nearly. The diameter does need to match, but you also need to consider the materials -- metal needs grease, carbon fiber doesn't, so combining the materials in the frame and seatpost shouldn't be done.

Also, note that different seat posts have different levels of adjustability - saddle angle and position, height (which connects to minimum/maximum insertion distance) to name some, so your seatpost will need to be adjustable enough to get a good fit for you.

As for saddles fitting on the seat post, most saddles will work with most seatposts as the rail width on the saddles is essentially standard.

So, I'd say make sure your seat post is metal if your bike is metal, carbon fiber if your bike is carbon fiber. Then, pick something with the same diameter and enough adjustability so your bike can fit on it (for most people, even a basic seat post like the Bontrager SSR seat post will work fine, though for nice saddles like Brooks, you will want something with a bit more adjustability).

  • My bike seat post (see one of the pics) says 25.4 mm ... but I measured 27.2 mm. Is this a big deal?
    – Dissenter
    Oct 20, 2014 at 5:26
  • I'd guess you measured wrong then. 25.4 mm seatposts can go into 27.2 mm bikes with a shim (such as the one from Problem Solvers). The reverse doesn't exactly work.
    – Batman
    Oct 20, 2014 at 5:31
  • So, I'd guess that the right diameter is whats on the seat post - 25.4 mm.
    – Batman
    Oct 20, 2014 at 5:44
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    The "little thing" clamps the seat rails to hold the seat. If you get the "simple sticks" you need to clamp a clamp onto the stick to clamp the seat on using the rails on the seat. It's lot easier to get the former.
    – mattnz
    Oct 20, 2014 at 8:48
  • 1
    I'd recommend getting the one with the "little thing" - it makes adjusting the saddle easier (also, spending a bit more on one with a bit more adjustability may not be a bad idea). Also, make sure its appropriate in length so that you can place the saddle at an acceptable height.
    – Batman
    Oct 20, 2014 at 14:51

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