Road bike: top tube help!

Discussion in 'Beginners' started by Kr4t0z, 13 Apr 2010.

  1. Kr4t0z

    Kr4t0z New Member

    I'm planning on getting a new road bike, and I know most bikes' measures are C-T, and I don't know why people keep asking for the top tube measures. Although I've tried several bikes, it's been hard for me to determine whether me being comfortable or rather it's the way it should be. I'd say it's because I'm inexperienced and unable to deduce, so I thought I would seek some professional help.

    My question remains, How do I know what top tube length suits me best?

    I'm 5'7, and the bikes I tested had a C-T length of 52cm and 54cm, so I assume they're medium sized frames.

  2. Alien8

    Alien8 Senior Moment

    Getting yourself properly measured-up in a shop would give you the best data.

    It's because reach is usually the most critical factor in sizing a frame to a rider.

    Go for comfort - if you're not comfortable you won't want to ride the bike.

    If you found a comfy bike you need to know the equivalent or virtual top-tube length which is the length of the top-tube if it were horizontal (which of course it may be anyway). Some manufacturers will quote this figure or you could try and measure it yourself.
  3. GrasB

    GrasB Veteran

    Nr Cambridge
    The effective top tube (ETT) length defines you how much 'reach' you have. There's around 80mm of adjustment range if you change the stem with the last 15mm of that in the extremes having a negative effect on the bike handling. You want to get this more-or-less right as there's not much adjustment there.

    The C-T is a measurement of the seat tube, you can have up to 300mm of adjustment on a 400mm seat post. This gives lots of latitude for height adjustment making the C-T size less important than the ETT as there's a lot more adjustment available there.

    I my self have a shortish torso so tend to go for a bike a size smaller than you'd expect with most of a 350mm seat post exposed but crucially my stem will be in the 110-130mm range which is right in the middle of the stem range & a good compromise between steering stability & chuckability
  4. OP

    Kr4t0z New Member

    Thanks for replying. So i'd rather go for a 52cm C-T bike. I'm not sure about this but do bike stores adjust these stems accordingly like replacing etc. ?

    What if I decided to get a used bike instead? I mean I have a friend who's using a small frame size, 48cm, and we're about the same height, is it possible for me to got for that size or not really?
  5. Banjo

    Banjo Fuelled with Jelly Babies

    South Wales
    I found it hard to get the right size road bike.Problem is that standard bikes are made for standard size people and not many of us are.

    Reach is important but can be shortened or lengthened with a different stem which the bike shop will most likely swap foc for you as part of the deal.

    The seat post tube height dictates the amount of seat post you need to extend .Too much seatpost extended can lead to the bars much lower than the seat which means riding the bike in a more bent forward position which is ok if your young and supple but if your not so supple may lead to back and neck pain.

    When trying a bike out for size in the shop make sure they first set the seat at the correct height for you or you will get a false impression .
  6. ASC1951

    ASC1951 Guru

    Frame geometry is subject to fashion - noone had heard of sloping top tubes 20 years ago - so the top tube length is actually the most important fitting dimension on a bike.

    If you are getting a new bike and paying a fair whack for it (say £500+) I would recommend getting it from a shop with a fitting jig if you can. A fitting session is usually about £50 but most shops will give it you free if you get a bike from them. Keep the printout and it will save you a fortune over the years.
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