Determining Bike Size

Discussion in 'Cycling Equipment' started by David_Zen, Jun 2, 2004.

  1. David_Zen

    David_Zen New Member

    Joined:
    Jun 23, 2003
    Messages:
    79
    Likes Received:
    0
    I don't yet have a road bike but the mountain bike I ride is a size 17 inches. I am about 5 ft 7 inches tall. I know someone who is selling a Trek road bike that is a size 50 cm. How do I determine if this bike is a good size for me? I know it's not too big. The person is selling at a good price and I would like to buy but the size issue is the only thing that has me hesitating.
     
    Tags:


  2. jhuskey

    jhuskey Moderator

    Joined:
    Oct 6, 2003
    Messages:
    10,533
    Likes Received:
    291
    Just as a guess I would say a 52- 53 cm would fit you better and there are a lot of factors.People vary in anatomy one persons legs may indicate a 31 inch standover and another a 33 inch and they could be the same height and then there is the stem length, seat position,bar width,the type of riding you do and so on. Without going to a bike shop for sizing I suggest riding the bike and if it feels right it probably is ok.:confused:
     
  3. David_Zen

    David_Zen New Member

    Joined:
    Jun 23, 2003
    Messages:
    79
    Likes Received:
    0
    Thanks, I'll probably go see the bike and take it for a test ride.
     
  4. ed073

    ed073 New Member

    Joined:
    May 19, 2004
    Messages:
    1,528
    Likes Received:
    0
    Frame size (centre-to-centre) can be calculated by:

    Inseam length in socks, feet about 15cm apart
    x
    0.65

    Saddle height (top of saddle to centre of BB) should be the same inseam measurement x 0.885....but use this as a starting point only. Make small changes until you feel most comfortable

    Good enough for Greg LeMond.
     
  5. Cipher

    Cipher New Member

    Joined:
    Sep 7, 2002
    Messages:
    783
    Likes Received:
    1
    You might want to read this by Sheldon Brown as well as other links on the subject of proper bike fit at the end of his article.

    http://sheldonbrown.com/frame-sizing.html
     
  6. tafi

    tafi Member

    Joined:
    Jul 31, 2003
    Messages:
    1,038
    Likes Received:
    16
    Unfortunately not good enough for a lot of others. Anyone who is not "average" (what ever that means) in proportion will find it difficult to fit a bike sized on their inseam.
    I take myself as an example. Depending on which way you look at it I have either a long pair of legs or a short torso for my height. My legs are long enough (according to Lemond's formula) to fit a bike with a 57cm seat tube. However based on my own experience I need somewhere around a 52~54cm top tube. If I rode a bike built by Lemond with the right seat tube I would be riding a 57 or 58 cm top tube way too long. similarly the 58cm trek that I'd also fit would be too long aswell. You can shorten the stem but I wouldn't go any shorter than 10cm (particularly on a steep American bike) because it will get more twitchy to handle.

    I would mbe more inclined to size a bike based on Top tube measurement.
    I curently ride a 54cm Trek with a MTB seatpost and a 10cm stem with a lot of stack height to get close to the posi I need.

    A good formula for top tube (cm) is approximately given by (very approximately):
    TT=(torso length+arm length)/2 + 4 - (stem lenghth)

    For me this estimated a little on the short side but it can vary a bit based on what seat tube angle you decide to use and how far back your saddle has to be. The ultimate test is getting on the bike.
     
Loading...
Loading...