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Seatpost size

  • 20-10-2017 7:02pm
    #1
    Muckers
    Registered Users, Registered Users 2 Posts: 504 ✭✭✭


    Hi all. What is the standard seatpost clamp size for a road bike. When measuring the diameter of the seatpost is it the inside or outside measurement that is used.


Comments

  • #2
    Type 17
    Registered Users, Registered Users 2 Posts: 2,731 ✭✭✭Type 17


    Seatpost clamps are measured at the outside of the frame/inside of the clamp. Common sizes are 31.8 & 34.9mm, but the exact size of your bike's one can't be predicted based on its make or type, you'll just have to measure the old clamp or frame.

    Seatposts are measured at their outside diameter - there are loads of sizes between 25.0mm and around 31.8mm. You'll need to get the exact size, as a mis-match as small as 0.2mm is enough to mean a post is too big/small.


  • #3
    Muckers
    Registered Users, Registered Users 2 Posts: 504 ✭✭✭Muckers


    Type 17 wrote: »
    Seatpost clamps are measured at the outside of the frame/inside of the clamp. Common sizes are 31.8 & 34.9mm, but the exact size of your bike's one can't be predicted based on its make or type, you'll just have to measure the old clamp or frame.

    Seatposts are measured at their outside diameter - there are loads of sizes between 25.0mm and around 31.8mm. You'll need to get the exact size, as a mis-match as small as 0.2mm is enough to mean a post is too big/small.

    Cheers thanks for that. I bought a 34.9mm clamp online and it said in the description that it fits a 31.8mm seatpost. It's slightly too small to fit down over the seat tube. Back to the drawing board


  • #4
    Type 17
    Registered Users, Registered Users 2 Posts: 2,731 ✭✭✭Type 17


    Bear in mind that the paint on the seat tube may be thick, and can cause things to be a bit tight. Remove the bolt from the new clamp and stretch it open a little (a few extra mm at the jaws of the clamp) whilst trying to fit it over the seat tube. If you're not close even then, it's the wrong clamp.


  • #5
    Muckers
    Registered Users, Registered Users 2 Posts: 504 ✭✭✭Muckers


    Type 17 wrote: »
    Bear in mind that the paint on the seat tube may be thick, and can cause things to be a bit tight. Remove the bolt from the new clamp and stretch it open a little (a few extra mm at the jaws of the clamp) whilst trying to fit it over the seat tube. If you're not close even then, it's the wrong clamp.

    Hi just measured my seatpost and it's 35mm on the outside. Hence a 34.9mm clamp won't fit. It's a Wilier frame. Is this an unusual sized seatpost.


  • #6
    Type 17
    Registered Users, Registered Users 2 Posts: 2,731 ✭✭✭Type 17


    Is it the seat post or the seat tube (the frame) that is 35mm?


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  • #7
    Muckers
    Registered Users, Registered Users 2 Posts: 504 ✭✭✭Muckers


    Type 17 wrote: »
    Is it the seat post or the seat tube (the frame) that is 35mm?

    Sorry my error. The seat tube (frame) is 35mm


  • #8
    Muckers
    Registered Users, Registered Users 2 Posts: 504 ✭✭✭Muckers


    Muckers wrote: »
    Sorry my error. The seat tube (frame) is 35mm

    The seat tube is actually 34.9mm according to the maufacturer. But the 34.9mm clamp I bought is too small. It actually only measures 34mm on the inside and I don't want to damage the frame by attempting to force it


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