Sizing a TT Bike

Ed McC
Ed McC Posts: 175
edited January 2008 in Workshop
I have been told that a TT bike should have a frame size 2cm smaller than my regular road bike. Is this correct?

Comments

  • John.T
    John.T Posts: 3,698
    No. Like any bike it should fit you. Depending on the frames geometry it may be the same size or considerably smaller. It is unlikely to be bigger. Setting a TT position is more difficult than a road one as you are adding aerodynamics to the comfort / power equation. If you look at photos taken at a TT you will see all sorts of positions, some looking terrible but they seem to work. Most of us could not handle the positions that top pros ride so it is a bit of a compromise..
    My Fleet.
  • andrewgturnbull
    andrewgturnbull Posts: 3,861
    John.T wrote:
    No. Like any bike it should fit you. Depending on the frames geometry it may be the same size or considerably smaller. It is unlikely to be bigger. Setting a TT position is more difficult than a road one as you are adding aerodynamics to the comfort / power equation. If you look at photos taken at a TT you will see all sorts of positions, some looking terrible but they seem to work. Most of us could not handle the positions that top pros ride so it is a bit of a compromise..

    Hi there.

    John is right. But your original advice is probably correct too. Most people find their best aero position with a top tube that is slightly shorter than on their road bike. For example, my road racing frame is a 56, my TT bike a 55.

    Your mileage may vary - if you're not sure then go get yourself fitted before you buy a new bike.

    Cheers, Andy
    http://www.andyturnbull.co.uk
    http://www.stirlingtri.co.uk
  • aracer
    aracer Posts: 1,649
    The other point being that you'll probably want a shorter headtube to get low enough, However the geometry and position of a proper TT bike is sufficiently different from a road bike that using a normal road frame will always be a compromise.
  • Monty Dog
    Monty Dog Posts: 20,614
    As said, reach i.e. toptube length and height i.e. headtube length are more critical - your toptube will be shorter than your normal road bike, but the limit is usually defined by your knees hitting the bars when out the saddle. Getting low enough is mainly dictated by your flexibility rather than the bike frame - besides it's a law of diminishing returns when your thighs start getting near to your chest. Some TT frames have a slightly steeper seat tube angle too to allow the rider to engage the glutes and quads - this again can result in a shorter reach too. However, too forward a position can create handling problems with all the weight over the front wheel, making it more inclined to wash-out on corners.
    Make mine an Italian, with Campagnolo on the side..
  • aracer
    aracer Posts: 1,649
    ...hence the proper TT frame which is designed from the outset to be used with such a position.

    If you're using tri-bars then you need the tops where they bolt on to be lower than the tops of normal road bars just to get the same position as when using drops - hence why head tube length is an issue even for those without extra flexibility.

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