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How do I measure...?

janetthompsonjanetthompson Posts: 82
edited October 2008 in Road beginners
How do I measure the frame size of the bike I already have? Is it the base of the seatpost to the bottom of the frame, or is it to the floor?
Thanks

P.s. Sorry for the silly question
Not lost, just exploring...

Posts

  • N4PALMN4PALM Posts: 240
    edited October 2008
    Measure from the center of the bottom bracket to the top of the seat tube.

    OR/AND

    Measure it from the center of the bottom bracket to the center of the point where the top tube and the seat tube meet.

    These are the 2 main ways that manufacturers measure their frames.
  • BronzieBronzie Posts: 4,927
    ............but if your frame has "compact geometry" (ie sloping top tube) quite often the manufacturer's quote an "effective frame size" ie what size the frame would be if the top tube was horizontal rather than sloping.

    So no, not a silly question at all, but there are a number of ways frame size is quoted by different manufacturers.
  • andy_wrxandy_wrx Posts: 3,396
    8OCRComp.jpg

    Yes.
    - some will measure the seat-tube from centre of bottom bracket to top of seat tube : A in diagram above
    - but some will measure from centre of bottom bracket to top of top tube (aka 'crossbar') where it joins seat tube
    - and some will vary this slightly by measuring to the centreof the top tube where it joins seat tube
    - and as Bronzie says, on a compact frame others will measure by either of the two latter methods but using an imaginary horizontal top tube rather than the real sloping top tube.

    So two 56's from different manufacturers might be totally different sizes, a 54 from one manufacturer might be the same as a 58 from another.

    What make is your bike ? Would be worth going on that manufacturer's website and seeing if there's a 'Geometry' tab which has a picture similar to that above, then you can look where 'length A' runs from on their picture.

    Just for amusement, I don't know what method Softride use for their frames :P
    14-N0001.jpg
  • Big Red SBig Red S Posts: 26,890
    andy_wrx wrote:
    Just for amusement, I don't know what method Softride use for their frames :P
    I've found myself wondering that before
  • andy_wrx wrote:
    8OCRComp.jpg

    Yes.
    - some will measure the seat-tube from centre of bottom bracket to top of seat tube : A in diagram above
    - but some will measure from centre of bottom bracket to top of top tube (aka 'crossbar') where it joins seat tube
    - and some will vary this slightly by measuring to the centreof the top tube where it joins seat tube
    - and as Bronzie says, on a compact frame others will measure by either of the two latter methods but using an imaginary horizontal top tube rather than the real sloping top tube.

    So two 56's from different manufacturers might be totally different sizes, a 54 from one manufacturer might be the same as a 58 from another.

    What make is your bike ? Would be worth going on that manufacturer's website and seeing if there's a 'Geometry' tab which has a picture similar to that above, then you can look where 'length A' runs from on their picture.

    Just for amusement, I don't know what method Softride use for their frames :P
    14-N0001.jpg


    It's a Dawes Giro 400, and I think the frame is 47cm. (Their website is flaming useless). I'm looking to upgrade to an Orbea Onix, but their smallest frame size is 48cm, and I don't know how much difference that 1cm would make as I have pretty short legs. My nearest Orbea stockist is 40 miles away, so I'm thinking I probably need to take a drive up there and test one for myself.

    Thanks for your help :)
    Not lost, just exploring...
  • andy_wrxandy_wrx Posts: 3,396
    See http://www.dawescycles.com/files/new_08 ... ries-2.xls
    - row 201

    If you have a Giro 400 size 48 (there is no 47), then it says Seatpost Length 480mm

    That kind-of suggests they are measuring like in the diagram above and measurement A is 480mm.
    Effective Top Tube will be D and 540mm, Headtube Length is E and 110mm, Wheelbase is G and 1032mm, etc.



    You say you have short legs....
    To be honest, quite how high the saddle is isn't much of a problem, particularly with compact/semi-compact frames where you have quite a bit of seatpost sticking out of the frame - you can always move this up or down a centimetre or two.

    What's maybe more of an issue is how long the frame is - that 'effective toptube length' D.
    If this is too long or short, this is what makes the bike too big/small for you as it's far more difficult to adjust than just shoving the saddle a bit higher/lower.
    Note how it's 'effective toptube length' : if the toptube is sloping on a compact frame, you don't measure straight along it, you do need to measure an imaginary horizontal top tube to where it meets the seat tube.

    If you have an Orbea dealer, it might be worth the trip and get their view on fitting, particularly as you're a woman and so might be a slightly different fit than a man (different leg/arm/torso/etc ratio) : although no-one alive is 'average' !
  • andy_wrxandy_wrx Posts: 3,396
    Big Red S wrote:
    andy_wrx wrote:
    Just for amusement, I don't know what method Softride use for their frames :P
    I've found myself wondering that before

    Yeah, so do you want the Forward Aero position, Big Slam poosition, or Road position ?

    Must be a complete different ballgame to get a fitting on a Softride because you can slide the saddle along the beam and change the geometry as well as the sizing...
  • John.TJohn.T Posts: 3,698
    I would always recomend a test ride anyway as there is a lot more to how you feel on a bike than just size. Top tube length is also important, some (me included) would say more so. How it actualy feels on the road and how you like its stiffnes or lack of it also matter.
    The Orbeas do look very nice so it is definately worth a 40 mile trip. If you book a test you may get to ride a fair distance. I managed 65 miles on a demo Trek Madone 5.2 but they made a sale so it was worth their while. You may struggle getting a small one to test though. Ring them first.

    Must type faster.
  • hopper1hopper1 Posts: 4,389
    You can compare the measurements on andy_wrx diagram with this one
    onix-g.jpg.
    I'm sure that a call to your local Orbea dealer would be of help to you.
    I know that Epic Cycles do have small demo bikes, but they are quite a hike from your area.
    Start with a budget, finish with a mortgage!
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