I am having someone build a Muni frame for me and I want to pick
an appropriate seat tube diameter.
In order to save cash, I was going to use my miyata seat post and shim it up to fit a 25.4mm ID. I was thinking that this might allow me to upgrade to a railed seat post plate later on if I wanted to .
What diameter would you recommend and why?
Work the maze.
27.2 because it is the most standard size for good seatposts. Unicycle.com has shims that will let you fit a Miyata 22.2 mm seatpost in a 27.2mm seat tube. Later on when you want to upgrade the seatpost you will be glad to have the 27.2.
25.4 is used for BMX but not often used for MTB. You’ll have a harder time finding a quality seatpost in 25.4.
The 27.2 will give you a larger area to clamp which will hold better.
The only advantage I can see for a 25.4 post is that you could find a beefy two bolt BMX seatpost clamp that might fit. A double bolt clamp would (should) hold the seatpost very well.
25.4 is where the rail types start(this was the standard for B.M.X for yearz
however,the world is a bigger place now and posts of that size make me cringe.there are not as many options in 25.4.if i had to choose, it would be 27.2 becauze it haz been a road bike standard for decades.
thompson makes all the sizes so i guess to me:it comez down to options and taste.i like the way a fatter post looks,it tends to balance out that huge 3 inch tire down there
along with another member of this board, i raced BMX for a number of years. I have 3 bikes sitting in my garage back home. So I could theoretically put one of those seatposts w/ a BMX seat on the Uni?
I have a Primo 7/8" seatpost on my Coker. I already had a carbon seat fit with the rails and I wanted to put it on the Coker. A 7/8" BMX post worked OK for that but the post is a snug fit in the Coker. It is a heavy seatpost. If it was on anything other than a Coker I would prefer a lighter aluminum post instead of tube of steel they use for BMX posts.