Seatpost shim?

Mulletus Maximus
Mulletus Maximus Posts: 11
edited June 2008 in Workshop
Hi all.
I have a Bianchi 1885 and i'm wanting/ needing to get a new seatpost.
My seat post size is 31.4mm so i'm going to need a shim. The post i'm looking at comes in sizes of 27.2 & 29.4.
My question is, what size shim do i need based on the above post sizes?
Would this -27.2 to 31.4 be the correct size?
All replies and help greatly appreciated.
Cheers. MM

Comments

  • blorg
    blorg Posts: 1,169
    If your frame seat tube inner diameter is 31.4mm and you want to use a 27.2mm seatpost, then yes, although bear in mind that the two most common seatpost sizes are 27.2 and 31.6 so I would just double check that you definately have a 31.4 rather than a 31.6 seat tube.

    Indeed a quick check on the net and this review of the 1885 suggests it has a 31.6mm post.
  • Mulletus Maximus
    Mulletus Maximus Posts: 11
    I originally thought It was 31.6 which would make things very easy but i've also heard from poeple that it is 31.4 and unless i've missed it, it doesn't say on the existing post.
    I guess i need to get hold of a digital vernier caliper and measure it.
    Thanks for the info on the shims. It's obvious when you know!!!!
  • itisaboutthebike
    itisaboutthebike Posts: 1,120
    best shim (IMO) are USE ones.
  • blorg
    blorg Posts: 1,169
    I'd be suprised if it doesn't say somewhere on the original post, I've never had a post that didn't - should be listed along with a Ø. Probably at the bottom of the post, e.g. you will have to take it out of the frame :D

    I have a 31.6-27.2 USE thermoplastic shim myself (wanted to keep all my seatposts at 27.2) and it works fine although you do have to tighten a fair bit to prevent slipping.
  • Mulletus Maximus
    Mulletus Maximus Posts: 11
    You were right blorg. It is indeed 31.6, which makes buying a post so much easier.
    I need to buy a post with setback. Is the setback measured from the centre of the post to the centre of the seat clamp.?
    Thanks in advance?
    MM
  • blorg
    blorg Posts: 1,169
    Mulletus Maximus wrote:
    I need to buy a post with setback. Is the setback measured from the centre of the post to the centre of the seat clamp.?
    Yes, that's it. Most commonly seatposts will have setback and the most common amount is 20mm although you can get inline or 5/10/15/25mm posts. Above that is possible but it is less common. Bear in mind you can have quite a bit of adjustment with your saddle rails (depending of course on the saddle.)

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