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  1. #1
    Donnie Jonhson
    Join Date
    Mar 2014
    Location
    Australia
    My Bikes
    Many, mostly old, steel, heavy and beautiful + one titanium bike; pretty much the complete opposite of my other bikes.
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    Seat post diameter for new titanium Audax bike

    Hi Everyone,

    I am in the process of building a high end titanium Audax/ultra distance bike. The bike has been assembled and riding perfectly, beyond what I ever expected.

    In the process of building the bike I borrowed the 27.2 diameter Ritchie seat post form my mountain bike and installed it with a 27.2-30.9 Crane Creek shim. The frame requires a 30.9 diameter seat post. I did this as a the frame geometry (seat tube angles) are different to my usual bike and I was unsure what set back I would require.

    Now that the bike a assembled and being ridden, it is time to purchase a new seat post. I am primarily considering an aluminium seat post however will consider a carbon one.

    My questions are;

    Should I purchase a 30.9 diameter seat post or continue to use the 27.2-30.9 shim and a 27.2 seat post?
    Will there be any noticeable difference between a 27.2 and 30.9 seat post?
    Have people experienced any problems with their frame when using a shim and a smaller seat post?

    Kind Regards

    Donnie Johnson

  2. #2
    Senior Member
    Join Date
    Aug 2007
    Location
    NorCal
    My Bikes
    2009 Surly Cross Check Frankenbike
    Posts
    513
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    I predict the consensus will be that:

    1. There is no advantage to your current arrangement, and maybe some mild disadvantages.
    2. You need to buy a new seatpost anyway, it doesn't really make sense to buy anything but the right part to put on a high-end bike you just had built.

    Of course, it's your bike, so you can do what you want.

  3. #3
    Senior Member
    Join Date
    Dec 2005
    Location
    Auld Blighty
    My Bikes
    Early Cannondale tandem, '99 S&S Frezoni Audax, '65 Moulton Stowaway, '52 Claud Butler, TSR30, Brompton
    Posts
    2,176
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    A larger diameter post may be stiffer than your current arrangement.

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