top tube lengths

mancjon
mancjon Posts: 53
edited August 2011 in Road beginners
Firstly apologies for such a basic question.

i know the best thing to do is to try bikes out but i was hoping to get a rough idea of how road bikes are sized.

I am a mountain biker, 6ft dead on with a 33" inseam. I have found the best effective top tube length for me is about 610mm on an mtb.

I am looking at getting a road bike but getting a bit confused as it seems a 56/58cm top tube is pretty much what is recommended for me but this is quite a bit shorter than what i am used to on an mtb. So obviously there is something i am missing. Could anyone shed some light on this for me ?

One other question. I was looking at the Giant Defy and from the sizing chart i seem to be able to use either a M/L or a L. If there are any Defy riders with my sort of dimensions could you let me know which one you went for ?

Any and all advice is much appreciated

Comments

  • Wheelspinner
    Wheelspinner Posts: 6,695
    MTB's have MUCH slacker seat tube angles, typically 67 - 68 degrees, versus a typical road bike around 73. That means the effective top tube length will be longer than a road bike, if your saddle height is the same on both machines, measured from crank centre to top of saddle along the seat tube line.

    Just a geometry thing.

    Also, don't forget that road bikes tend to have a stem that is at least 100mm long, often more, whereas MTB are usually around 100 max. Then you add the fact that road bars add an additional "reach" of another 80 - 120 mm in front of the stem to where your hands typically sit on the hoods, so when you add that on, your reach to the hoods from the saddle will be a lot longer than on the MTB.
    Open One+ BMC TE29 Seven 622SL On One Scandal Cervelo RS
  • Monty Dog
    Monty Dog Posts: 20,614
    As a starting point, take about 50mm from your MTB toptube length. As said, differing geometry plus the combined length of the road stem, bars and hoods and saddle setback means road bikes are generally more stretched-out, despite having a slightly shorter frame length.
    Make mine an Italian, with Campagnolo on the side..
  • topdude
    topdude Posts: 1,557
    One other question. I was looking at the Giant Defy and from the sizing chart i seem to be able to use either a M/L or a L. If there are any Defy riders with my sort of dimensions could you let me know which one you went for ?

    I think as you say either would be ok, i ride a M/L Defy and i am 5' 8" so maybe a L is better for you, (you need to try both sizes for yourself)
    He is not the messiah, he is a very naughty boy !!
  • garzar
    garzar Posts: 11
    As above you really need to try both. I'm 6'2" and I find my M/L perfect for me. I tried both and felt too stretched out on the L. I know this doesn't help with internet shopping but there's plenty Giant dealers around.
  • Chris James
    Chris James Posts: 1,040
    I can't comment on Giant sizing as I have never ridden one, but i am 6 foot with 33 in inseam.

    I ride a 57cm horizontal top tube frame with 110mm stem.

    Most manufacturers of compact frames would put me a on a 'large' frame.
  • mancjon
    mancjon Posts: 53
    Thanks to all for responding, much appreciated.
  • rafletcher
    rafletcher Posts: 1,235
    Fashions change. II'm the same size as I was 20 years ago, 5' 11" and 33" inseam. Then sizing was 60cm frame plus 12cm stem. Now I'd probably be recommended a 56cm top tube and 10cm stem. Go with what suits.
  • www.richtreen.co.uk
    www.richtreen.co.uk Posts: 245
    6' 2" Here and riding a large Defy, did fit a shorter stem as I am long in the leg and short in the body.
  • Chris James
    Chris James Posts: 1,040
    rafletcher wrote:
    Fashions change. II'm the same size as I was 20 years ago, 5' 11" and 33" inseam. Then sizing was 60cm frame plus 12cm stem. Now I'd probably be recommended a 56cm top tube and 10cm stem. Go with what suits.

    Your 60cm frame may have had a shortish top tube? In the old days the top tube often didn't increase propotionally with the seat tube, so you just fitted longer stems.

    I had a 24 inch frame in th 80s that had a shorter top tube than my current 57 s/t 57 t/t.
  • MichaelW
    MichaelW Posts: 2,164
    Measure your reach from saddle nose to the grip of your bars, where the web of your hand fits.
    If you want to ride in the same position as your MTB, this is the measure you have to replicate. With differeing angles and the extended bar design of a drop bar vs flat, and different grip length for various brake levers it is hard to tell without measuring in the metal. Get you and a tape measure to a bike shop.

    You may want to ride a roadbike in a different position.
    I transfer positions exactly by making an [x,y] graph of the points of contact, with the bottom bracket at [0,0]. use a plumb-line and a rule.

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