Frame Size

rcolliee
rcolliee Posts: 17
edited April 2015 in MTB buying advice
Hi,

The optimal frame size for my body measurements is 21" but I was wondering how precise it has to be? Would a 20" frame be fine? There are 2 bikes I am considering, one is a 20" frame and the other is a 21" frame but the 20" frame bike has slightly better specs. Should I go for the slightly smaller frame size and better specs or the correct frame size and not as good specs? I sat on the 20" frame bike today and it felt fine, my arms were slightly bent in the cycling position.

Comments

  • dj58
    dj58 Posts: 2,217
    For offroad riding it can be advantageous to have a smaller frame, less weight more manoeuvrable, so if you prefer the 20" bike buy it, but double check your measurements first.
  • kajjal
    kajjal Posts: 3,380
    Optimal frame size calculations are really just a rough guide. In the end it is the bike you feel fits you best, rides well, has a good spec for the price and you like the look of.
  • cooldad
    cooldad Posts: 32,599
    There is no such thing. Manufacturers measure bikes differently, and even measure different models differently.
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  • The Rookie
    The Rookie Posts: 27,812
    As top tube length is more important to how a frame suits you than the nominal length of the seat tube (which can then be adjusted by circa +10" using the seat post), then anyone claiming there is an optimal frame size by that measurement is talking BS.

    Add in the fact that most manufacturers make the bikes in 2" increments so only half of them will be even making a 21" the other half will expect a 20 or 22" to suite and you can further see it's obvious BS.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • peter413
    peter413 Posts: 5,120
    DJ58 wrote:
    For offroad riding it can be advantageous to have a smaller frame, less weight more manoeuvrable, so if you prefer the 20" bike buy it, but double check your measurements first.

    It can also be advantageous to have a larger frame :wink:

    As others said, one manufacturers large isn't the same as another's. I'm 5'11" and ride both an 18" frame and a 21" frame. Both fit me properly. I completely ignore seat tube size until I've looked at the reach and top tube lengths along with everything else. The only thing I check the size of the seat tube for is to check I can fit my seatpost.
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  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    Seat tube length is fairly irrelivent. Top tube length is far more important. Personal preference also comes in to it.
    Personally I have had medium, large and extra large bikes with seat tube lengths between 18" & 21" and they all fitted me very well.
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  • kajjal
    kajjal Posts: 3,380
    Comparing my mid 1990's XC bike with my recent xc bike of similar size, they are very different bikes. The handling on the older bike is a lot twitcher due to the long stem and narrow bars, which for the time were wider than most. 26" wheels on the old bike are very different to the 29" wheels on the newer bike. Strangely the older bike is smoother to ride (steel frame) and also has smoother gear changes but is frightening over really rough stuff.

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