I have a 1990’s steel Giant frame. I bought it about 15 years ago, and the seller had installed a 27.0mm seat post. I have over time adjusted that seat post in height and always noticed how hard it was to move it within the seat tube. Now I need to replace the seat post. Without giving it sufficient thought I had bought a 27.0 post, which doesn’t fit.
After some research (Sheldon Brown’s seat post size database included) I suspect the actual seat post size should be 26.6. When I look at my current seat post I can tell that the years have worn down the diameter of the original seat post: I can start to see the aluminium “silver” color come through the black. I wonder if the steel seat tube inner diameter has also worn down a bit.
Now I have a dilemma: do I buy a 26.6 seat post as I suspect that is the intended size, or should I expect some wear on the inner diameter of the seat tube and buy a 26.8 instead?
I tried to measure the the inner diameter of the seat tube, but my non-digital calliper isn’t accurate enough to pick up on 1/10mm.
I am risk averse in this, so: if the 26.8 is too wide I have to force it in, if 26.6 is too narrow I have to over tighten the integrated seat post collar. Which would be worse from fatigue perspective?
Unfortunately I don’t feel this is going to solve my problem immediately: firstly the calliper is a cheap plastic thing that I wouldn’t trust with anything more precise than a mm and secondly I am only able to measure the immediate entry of the seat tube and this can even fit the new 27.0 seat post for about 2cm deep.
I used my newly gained knowledge to measure the original seat post with my plastic calliper. It measures 26.8. Seeing it moves very tightly, I am going to try my luck with a new 26.6 post. Worst case it would be time to open a can of beer.