AI6YR Ben
Arghh.... how many different sizes are there of bicycle seatposts?!?! 😬 #BikeRepair #BikeTooter
Nov 24 at 12:16amWeb
Show threadEric GoodwinNov 24
@ai6yr so many!
Show threadLovesTha🥧Nov 24
@ai6yr And such meaningless differences. For a seatpost, anything less than a 10% change in size is only done to be incompatible.
Show threadJoshua ThayerNov 24

@LovesTha @ai6yr I can’t speak for more modern (carbon) bikes, but seatpost diameters are based on the inside diameter of the seat tube. When building a frame, framebuilders have two basic parameters to consider when selecting the main triangle tubes (including ST): outside diameter, and wall thickness. Those choices impact a bike’s suitability for its intended purpose and rider.

So, seat post outside diameter is downstream of choices the framebuiler makes for designing suitable bikes.

Show threadJoshua ThayerNov 24
@LovesTha @ai6yr Of course, one of those choices should include “availability of parts that will fit the bike”!
Show threadGary @N8DMTNov 24
@ai6yr N+1, where N is all the posts you have and the +1 is for the bike in front of you. (Digital calipers are helpful to finding one that fits properly.)
#SeatPostLotto
Show threadAI6YR BenNov 24
@n8dmt Sigh, I'm going to have to invest in a better caliper.
Show threadPaul SouthworthNov 25
@ai6yr @n8dmt Trying to measure a seat tube that is mangled at the top can also be quite a challenge even with a good caliper. The seat post sizing tool might work better for you.
Show threadAI6YR BenNov 25
@pws @n8dmt LOL I have officially scrapped this frame, I am unwilling to do more lye chemistry to try to dissolve it... and the top of the tube is now really mangled. Moving on to build a franken bike with its components on another frame, LOL.
Show threadRichard W. Woodley ELBOWS UP 🇨🇦🌹🚴‍♂️📷 🗺️Nov 24

@ai6yr

infinite ?

Show threadfreiheit🤖Nov 24
@ai6yr My favorite is that there’s sizes w/ 0.2mm difference, so hard to tell apart but just enough size difference to not work if you get it wrong
Show threadAI6YR BenNov 24
@freiheit Yep, this is what I find myself working with.
Show threadfreiheit🤖Nov 24
@ai6yr 27.0 or 27.2?
Show threadAI6YR BenNov 24
@freiheit Well, I have one at 27.2, but the other bike I need a seatpost to I thought was the same, but it is not. It is maybe 30.9, or 31.6, or 31.8... my measuring device is not accurate enough to tell on that one.
Show threadPeter McDonaldNov 24

@ai6yr Sheldon Brown is sadly long gone, but his website remains an incredible resource, especially for older bikes:

https://www.sheldonbrown.com/seatpost-sizes.html

Sheldon Brown's Seatpost Size Database

A database of seatpost sizes for various bicycles.

Show threadAI6YR BenNov 24
@pmcdonald LOL I am trying to replace the seat post (no longer existent) for an unlisted model, and look at the variability even in this one manufacturer! LOL.
Show threadAprilNov 24

@ai6yr Too many!

One of my favorite uncommon & absurdly expensive tools at a shop where I used to volunteer was similar to the Stein seat post sizing rods, though I think ours were from a different manufacturer. It seems you can get cheaper nylon ones now, which is nice to know!

Show threadisolNov 24

@ai6yr

How many sizes of which particular shape?
Just round ones to start with?

Tell Santa you need a complete collection of seatpost shims, and that you've been a good boy.🤪

Show threadMatt KronbergerNov 24
@ai6yr several.