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Bike sizing

  • 13-09-2015 10:31pm
    #1
    from_atozinc
    Banned (with Prison Access) Posts: 2,943 ✭✭✭


    My trek hybrid bike has a size written on it of of 22.5 inches / 57 cm, what is this length referring to ?

    I measured my top tube = 52cm, my seat tube = 48cm and my down tube = 58cm

    None of them were 57cm ??


Comments

  • #2
    Cee-Jay-Cee
    Registered Users, Registered Users 2 Posts: 12,235 ✭✭✭✭Cee-Jay-Cee


    It's generally the effective length of the top tube from the centre of the steerer to the centre of the seat post along a horizontal Plain and not along the actual tube itself which on many bikes is sloping/curved.


  • #3
    from_atozinc
    Banned (with Prison Access) Posts: 2,943 ✭✭✭from_atozinc


    Cee-Jay-Cee wrote: »
    It's generally the effective length of the top tube from the centre of the steerer to the centre of the seat post along a horizontal Plain and not along the actual tube itself which on many bikes is sloping/curved.

    Thanks my top tube is more a less horizontal.........but still way off 57 cm no matter how horizontal I do the measure.


  • #4
    nilhg
    Registered Users, Registered Users 2 Posts: 5,185 ✭✭✭nilhg


    You should be able to find a geometry chart for your exact model, but looking at this:

    http://www.trekbikes.com/us/en/bikes/road/fitness/fx/7_2_fx/

    it looks as if the 57cm refers to a notional measurement for the seat tube? Probably that's the out of the box Bb to saddle measurement?


  • #5
    from_atozinc
    Banned (with Prison Access) Posts: 2,943 ✭✭✭from_atozinc


    nilhg wrote: »
    You should be able to find a geometry chart for your exact model, but looking at this:

    http://www.trekbikes.com/us/en/bikes/road/fitness/fx/7_2_fx/

    it looks as if the 57cm refers to a notional measurement for the seat tube? Probably that's the out of the box Bb to saddle measurement?

    Thanks. Oh I dunno, wouldn't you think bike manufacturers would have a standard sizing guide across the board


  • #6
    gambeta_fc
    Registered Users, Registered Users 2 Posts: 149 ✭✭gambeta_fc


    Stack and reach are the numbers you're after if you want to compare across different bikes/brands. Measurements are relative to the BB. Most manufacturers will include it in their sizing guides or video below shows how to measure it on existing bike.

    https://www.youtube.com/watch?v=psbu9OH69sI


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  • #7
    TychoCaine
    Registered Users, Registered Users 2 Posts: 673 ✭✭✭TychoCaine


    Cee-Jay-Cee wrote: »
    It's generally the effective length of the top tube from the centre of the steerer to the centre of the seat post along a horizontal Plain and not along the actual tube itself which on many bikes is sloping/curved.
    No it's not. It's the seat tube length from the centre of the BB axle to the top of the top tube. The two tubes are usually within a couple of centimetres of each other anyway but it has to be said. :cool:

    The important measurement would be the seat tube length *if* the top tube were horizontal (i.e. like it was in the olden days). Frame size isn't as critical as it used to be because you have massive adjustability these days in seat posts and stem lengths. You have three points of contact with the bike (saddle, pedals & bars), and as long as these are in the right place (Ideally get a professional bike fit to identify these measurements) it doesn't matter much how you get there. It could be a big frame with a short slammed stem and a short seat post, or a small frame and a long stem, big spacer stack and long seatpost.


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