frame size

Discussion in 'UK and Europe' started by Jane, Mar 2, 2006.

  1. Jane

    Jane Guest

    What does this mean please?
    How is it measured?
    My daughter is 3ft 11" and I'm looking for a mountain bike for her 7th
    b-day. What size should I be looking at please?
    thanks
    Jane
     
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  2. Brian

    Brian Guest

    If you're looking at children's bikes, the size quoted is usually wheel
    diameter (adult bikes will have wheel diameter ~26" to 28"). Adult bikes
    are sold by frame size (normally quoted as the length of the seat tube).
    Your best option is to go into a decent bike shop and ask them, but for
    guidance, I would guess a 20" wheel would probably be about right.

    Brian

    Jane wrote:
    > What does this mean please?
    > How is it measured?
    > My daughter is 3ft 11" and I'm looking for a mountain bike for her 7th
    > b-day. What size should I be looking at please?
    > thanks
    > Jane
     
  3. Richard

    Richard Guest

    Jane wrote:
    > What does this mean please?
    > How is it measured?
    > My daughter is 3ft 11" and I'm looking for a mountain bike for her 7th
    > b-day. What size should I be looking at please?


    <glib answer> one that fits her </glib answer>

    It depends on your daughter's leg length and arm length, too.

    She should be able to easily straddle the top tube with her feet flat on
    the ground, with at least 3" clearance between crotch and top tube.

    If she's a confident capable cyclist already, you'll want to be able to
    lift the saddle height to the "usual" position, ie high enough that
    sitting on the saddle (and with the bike supported vertically by someone
    else) with the heel of one shoe on the lowermost pedal, with the pedal
    cranks orientated vertically. If she's less confident/capable as yet,
    the saddle will need to drop low enough that she can put one or both
    feet down on the ground.

    She should have a comfortable position sitting on the saddle and leaning
    forward to grasp the handlebars. If the bike is too large, she'll be
    leaning forward too much, stretching. (And whilst you're at it, make
    sure that the brake levers aren't too much of a stretch for her hands;
    most are adjustable in that manner).

    Don't be tempted to get something that's uncomfortably or dangerously
    large for her because "she'll grow into it"; she'll find it hard to
    control and thus it'll be an unenjoyable experience. Of course some
    'grow room' is useful.

    R.
     
  4. Simon Brooke

    Simon Brooke Guest

    in message <[email protected]>, Jane
    ('[email protected]') wrote:

    > What does this mean please?
    > How is it measured?
    > My daughter is 3ft 11" and I'm looking for a mountain bike for her 7th
    > b-day. What size should I be looking at please?


    It used to be that all adult sized bikes had similar frame geometries and
    so the if you fitted a bike of a given size from one manufacturer you
    fitted that size from any other manufacturer. But styles of bike have
    changed greatly in the last fifteen years and this is no longer so. I
    used to fit a 25 1/2" frame, and my old road bike is still that size;
    but my new road bike, which also fits me really well and has a
    horizontal top tube, is a 24" and my mountain bikes (sloping top tube)
    are 19".

    Children's bikes were never like this anyway, because there's never
    really been a standard frame geometry for kids bikes.

    If you don't want to take her to a bike shop (or don't have a local bike
    shop you trust to fit her properly rather than selling you whatever they
    happen to have in stock on the day), find a friend's bike that she's
    comfortable on, and CAREFULLY measure the distance from the axle of the
    pedal cranks ('bottom bracket') to the top of the seat along the seat
    tube; from that point on the seat to the centre of the handlebars; and
    from the centre of the handlebars to the bottom bracket. That triangle
    defines the fit of a bike, because it's at those three points (feet,
    bottom, hands) that the rider contacts the bike. Take the measurements
    along to the bike shop and get the largest bike than can be adjusted
    down to fit those measurements, so that she's got some growing time on
    it.

    --
    [email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/
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