Frame sizing - current frame vs new one?

101_North
101_North Posts: 607
edited May 2010 in MTB buying advice
Thinking of buying a frame online (can't buy it locally to try) but wanted to check the best way to measure up the size. I'm guessing the manufactures frame size is pretty much irrelevant as the geometry will vary regardless. If I was to meaure my current bike and compare it to a new frame what measurements would be most important to consider?

Cheers

101

Comments

  • The Northern Monkey
    The Northern Monkey Posts: 19,136
    The same measurments you can find for the frame you want to buy...
    Santa Cruz Butcher
  • nicklouse
    nicklouse Posts: 50,673
    first find out how the maker has measured their frames and then measure accordingly.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • 101_North
    101_North Posts: 607
    Right so...

    If measurement A equals (roughly) Measurement B over the frame I'm good to go?

    Are there any measurements where a slight variation can be ignored? I'm assuming top tube length is pretty important. What about headtube length? BB height? Seat tube - can I ignore that as height can be changed easily with a different post height?

    101
  • The Northern Monkey
    The Northern Monkey Posts: 19,136
    They will all give a frame different charachteristics.
    Also, as Nicklouse said, there is no standard way to measure a bike.... one manufacturers top tube length could be anothers effective top tube length, for example.
    Santa Cruz Butcher
  • 101_North
    101_North Posts: 607
    Ok. Here's what I've come up with:

    Current Frame:

    Size: 17"
    Head Angle: 70.5
    Head tube length: 11.8cm
    Seat angle: 73
    Top tube: 56.7cm (centre of headtube, horizontally back to the effective extension of the seat tube)
    C Stay: 42.5cm
    Wheel base: 104cm

    New frame:

    Size: 16.5"
    Head Angle: 70.3
    Head tube length: 11cm
    Seat angle: 73.3
    Top tube: 54.1cm
    Virtual top tube length: 56.2cm
    C Stay: 42.5cm
    Wheel base: 105.5cm

    Is the top tube measurement of the current frame (as described) the same measurement as the 'virtual 'tube length of the new frame?

    All in all they look pretty similar or am I missing something else?

    Cheers for the help folks.

    101
  • supersonic
    supersonic Posts: 82,708
    It looks similar but doesn't say what length fork the angles were measured with.
    GT ZASKAR CARBON TEAM

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  • 101_North
    101_North Posts: 607
    supersonic wrote:
    It looks similar but doesn't say what length fork the angles were measured with.

    Current bike came with 100mm forks. The new frame is described as "takes a 100mm travel fork" so I'm assuming it's measurements were based on this.

    The current frame is a Giant Terrago Disc and the frame I'm thinking of getting is a Kinesis Maxlight XC - only thinking though.

    Thanks

    101
  • supersonic
    supersonic Posts: 82,708
    Looks to be quite similar then. Though we all know a cm can make a difference :wink:
    GT ZASKAR CARBON TEAM

    VOODOO CANZO

    Come and see me at https://www.facebook.com/biketyke/
  • 101_North
    101_North Posts: 607
    supersonic wrote:
    Looks to be quite similar then. Though we all know a cm can make a difference :wink:

    LOL :D

    I really don't need a new frame as there's not much wrong with the Terrago. I've replaced every component on it though and it's just niggling away at me!

    Thanks for the advice folks.

    101

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