Forum home Mountain biking forum MTB workshop & tech

QR seat clamp size

hainmanhainman Posts: 699
edited June 2014 in MTB workshop & tech
Im back again and needing more advice,Im looking for new seat post clamp(qr) and cant figure out what size i'd need for a seat post that is 29.8 on my Rockrider 9.1,
Your wisdom would be greatly appreciated AGAIN
CRAIG
Giant Reign 2
Crohnie

Posts

  • cooldadcooldad Posts: 32,599
    Look on the current one - they normally have the size on them or measure the seatube. Seat post size is irrelevent.
    viewtopic.php?f=40073&t=12726337
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • hainmanhainman Posts: 699
    Thanks,my old one is manky and rusty and didnt know it had the size on it
    I'll take the post out and measure circumfirance of the seat tube,
    Giant Reign 2
    Crohnie
  • nicklousenicklouse Posts: 50,675 Lives Here
    why take the post out?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • hainmanhainman Posts: 699
    thought it easier to measure across the seat tube
    Am i meant to measure round ??
    Giant Reign 2
    Crohnie
  • cooldadcooldad Posts: 32,599
    cooldad wrote:
    Look on the current one - they normally have the size on them or measure the seatube. Seat post size is irrelevent.
    viewtopic.php?f=40073&t=12726337
    Yes.
    That's why I posted a link. It's easier.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • hainmanhainman Posts: 699
    Thanks will drag my bike out and measure it
    Now i can buy my shinny new red seat clamp and my qr skewers
    Giant Reign 2
    Crohnie
  • hainmanhainman Posts: 699
    So measured my seat post tube and its coming in at 36.3434
    Is this right or have I botched it some how.dont see any clamps that measure 36 mm
    Giant Reign 2
    Crohnie
  • cooldadcooldad Posts: 32,599
    Whar circumference did you get? Chances are it's 34.9.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • supersonicsupersonic Posts: 82,708 Lives Here
    It is the internal width of the seat tube, external width of the seat post.
  • hainmanhainman Posts: 699
    So measured it with bit of string,marked it and it was 115mm and when I do the divide its 36.6which is mahoosive.there was a 35 marked under the bottom of the clamp,so does it mean I can order 34.9 or is it bigger?.
    It's doing my head in,
    Giant Reign 2
    Crohnie
  • supersonicsupersonic Posts: 82,708 Lives Here
  • hainmanhainman Posts: 699
    Supersonic cheers I'll order that size and hopefully be right fit,just flung me abit when I got figures of over 36mm.all this for a shinny red seat clamp,better look good!!!! :D
    Giant Reign 2
    Crohnie
  • cooldadcooldad Posts: 32,599
    supersonic wrote:
    It is the internal width of the seat tube, external width of the seat post.
    Seriously? I think not. It's the external width of the seat tube.
    The external width of the seat post would errrr be the seat post size.
    Shirley?
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • hainmanhainman Posts: 699
    So it's not 34.9 i need...... :roll:
    Giant Reign 2
    Crohnie
  • cooldadcooldad Posts: 32,599
    hainman wrote:
    So it's not 34.9 i need...... :roll:
    It is - what was stamped on your clamp.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • hainmanhainman Posts: 699
    Was 35 on the underside and other letters and numbers but I was just stumped when my measurement by tape was 36.something
    I'll go with 34.9 and see how that goes might just get cheap one that way if its wrong I'm not faffing about returning stuff and trying to get money back for posting it
    Cheers guys for all your help
    Giant Reign 2
    Crohnie
  • cooldadcooldad Posts: 32,599
    99% of the time it will be a common size, and 34.9/35 is common.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • hainmanhainman Posts: 699
    Cheers cooldad
    Giant Reign 2
    Crohnie
  • supersonicsupersonic Posts: 82,708 Lives Here
    cooldad wrote:
    supersonic wrote:
    It is the internal width of the seat tube, external width of the seat post.
    Seriously? I think not. It's the external width of the seat tube.
    The external width of the seat post would errrr be the seat post size.
    Shirley?

    I thought he was clarifying the seat post size for some reason. All alu frames of 29.8 use a 34.9 seatclamp, so easy to tell from it.
  • Hijack.

    So, my seat post says 30.4 on it, I measured the outside of the seat tube, got 32mm

    What size QR should I need?

    There is a 31.8mm version of the QR I am looking at, is it outside of the seat tube you go by?

    Thanks.
  • jimothy78jimothy78 Posts: 1,407
    Forget the seatpost itself - the external diameter of the frame's seat tube is what's important. Very likely to be 31.8, but to double check, measure the circumference (around the tube) with a fabric tape measure (or a piece of string), then:

    9cm seat tube circumference = 28.6mm clamp
    10cm seat tube circumference = 31.8mm clamp
    11cm seat tube circumference = 34.9mm clamp
  • nicklousenicklouse Posts: 50,675 Lives Here
    jimothy78 wrote:
    Forget the seatpost itself - the external diameter of the frame's seat tube is what's important. Very likely to be 31.8, but to double check, measure the circumference (around the tube) with a fabric tape measure (or a piece of string), then:

    9cm seat tube circumference = 28.6mm clamp
    10cm seat tube circumference = 31.8mm clamp
    11cm seat tube circumference = 34.9mm clamp

    0.6mm ain't enough wall thickness for clamping area more likely to be bigger.

    But as we have no idea of the frame or even the material I will not guess the size as it could be anything.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • jimothy78 wrote:
    Forget the seatpost itself - the external diameter of the frame's seat tube is what's important. Very likely to be 31.8, but to double check, measure the circumference (around the tube) with a fabric tape measure (or a piece of string), then:

    9cm seat tube circumference = 28.6mm clamp
    10cm seat tube circumference = 31.8mm clamp
    11cm seat tube circumference = 34.9mm clamp

    Yeah 10cmm, bang on.

    Thanks.
  • RockmonkeySCRockmonkeySC Posts: 14,770
    hainman wrote:
    So measured my seat post tube and its coming in at 36.3434

    How did you measure to one tenth of a micron?
  • Really easy way. Take existing clamp into a shop and check with a human being who can match it.
  • Are we not human beings?

    I don't think you need to visit a shop for the simplest of things.

    Pretty confident I've got the correct size.
  • Chunkers1980Chunkers1980 Posts: 8,035
    Or just get some cotton wrap it around the outside, measure how long it is where the ends join and apply some maths.
  • Already done that.

    Don't see how visiting a shop is easier than that. Cause... it isn't.
Sign In or Register to comment.