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Thread: Which geometry?

  1. #1
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    Which geometry?

    Hi,

    I went to my local bike shop at the weekend for a road bike sizing. They use a wall mounted contraption to take my measurements and plugged these into bikefitting.com software. This output a recommended top tube size of 560mm, set tube of 542mm and stem length of 110mm. From this, the chap in the shop ruled out a few bikes (e.g. cannondale synapse and some others) based on the fact that in my recommended geometry, the reach is long compared to the ST. He suggested Bianchi frames would be a good fit (Impulso TT:550; ST:550 or Vertigo: TT:550; ST:540).

    Just out of interest I plugged my measurements taken during the sizing into the sizemybike android app that I'd recently installed. The recommended geometries were completely different. I was expecting some small differences, but was really surprised that the TT was nearly 5cm shorter the stem 2cm shorter. So I tried a third calculator: argonautcyclecoaching, but this gave me another different set of results.

    Needless to say I'm a tad confused about which of these is correct and whether the advice to buy a Bianchi is good (or whether any of this matters at all)!!!!

    Here are the measurements I used in each of the calculators: measurements.png

    Here's a summary of the main bike dimensions from each of the calculators: geometries.png

    Here are the images of the geometries:



    Any advice on this would be much appreciated.

    Other info... this will be my first road bike; I will be sportive riding (including the Etape this year) so am looking for something comfortable rather than with a racing geometry; my budget is 1000 - 1400 (so the Bianchi vertigo is at the top end of that range); I will buy through the cycle to work scheme which rules out some of the online options such as Rose and Canyon unfortunately; I am very fit and flexible (if that matters!).

    Many thanks in advance.

    TAO

  2. #2
    coprolite fietsbob's Avatar
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    Plane Geometry .. Just go test ride the Bikes and see what they Feel Like ..

    this will be my first road bike
    Doubly .. Hit the shops and ride what they have .

    You are confused because you dont have any experience .. and the internet over stimulates your Data Acquisition

    the more you spend the fancier the components will Be.

  3. #3
    Junior Member LarRig's Avatar
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    Don't get too wrapped up in all those measurement and charts. Just ride a few bikes you like and see what size feels best.

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    Senior Member AnthonyG's Avatar
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    All top tube lengths are not created the same. A top tube length of 550mm at a seat tube angle of 73 degrees is not the same as a top tube length of 550mm at 74 degrees. Totally different to the point that the number doesn't mean anything.

    The fitting program that gave a saddle setback distance makes the most sense, except that the leg measurements need to be VERY accurate to get a good answer. Failing that the quoted seat tube angle is next best, except I can't see how they calculated this angle. The size my bike fit calculator made the least sense simply because it didn't use enough data.

    For your purposed go with a bike that places the weight on the saddle and a little on the pedals. Avoid a bike that places too much weight on your hands/arms/shoulders. On a specification sheet you are looking for a more relaxed (smaller number) seat tube angle. Seat tube angles will be in a tight range from 72 to 75 degrees.

    Ride some bikes. Take note of how balanced you feel on the bike.

    Anthony
    Last edited by AnthonyG; 01-29-15 at 05:52 AM.

  5. #5
    Senior Member Dfrost's Avatar
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    BTW, 380mm wide bars are quite narrow. I'm very narrow across the shoulders and find I like my 42cm (Soma Highway One) bars better than the 40 or 44 (different brands and bends).

  6. #6
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by Dfrost View Post
    BTW, 380mm wide bars are quite narrow. I'm very narrow across the shoulders and find I like my 42cm (Soma Highway One) bars better than the 40 or 44 (different brands and bends).
    38 cm bars are not common, but his measurement is 38, and general guidance is to match the measurement. But there are some caveats -

    Were the shoulders measured correctly?
    Are the bars measured correctly?
    Is bar flare considered?
    What does the rider prefer?

    I think the last is critical. Wide bars are a style. As a young rider I bought was was out there, and now I'm pretty sure most of my high school bikes were around 38 cm. I'm reasonably comfortable on 40 Nittos and a little less so with 42's. In a randonneur bar I take a 45, which is about 37 c-c at the forward point of the hook.

    The bar width is a lot less critical, and easier to tune, than the stack/reach/seat tube angle.

  7. #7
    Fitter of road/ironman TriEngineer's Avatar
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    much of the information given by the apps and sites are bunk, they don't mean jack. frame reach/stack, which was given by the shop measurements, is the real steak (those numbers were 394/552), you weren't given a bike stack/reach and that's a shame.

    any other numbers given in those lists don't really mean much other than to just look at them, stack and reach has become a measuring point that many mftrs use to develop sizes.
    CAAD10 Ultegra 3 - CAAD10 - ELITE ROAD - ROAD - BIKES - 2015, size 54cm gives you (383/546)
    http://www.cervelo.com/media/docs/R2...09bc0b87-0.pdf, size 54cm gives you (378/555)
    TCR Advanced Pro 1 (2015) | Giant Bicycles | United States, size 50(m) gives you (386/552)

    I quickly took a look at the bikes that are popular here in north America. Based on those numbers, I would guess you are 5'7"-5'10" probably longer in the legs than torso. You say that you are flexible so your stack can be even less than 552, that's fine - spacers and angle of stem can change your BIKE stack (bike stack and frame stack is different, bike stack is the frame stack augmented by spacers, stem, etc.)

    I've picked up bikes that have a shorter reach than your 394, but again, this is frame reach, your BIKE reach will change once length of stem, seatpost setback is on.

    the 38 wide handlebars is BS, that's not possible. measure your acromial distance, size up to the next available one. Don't size down.

    Hope this helps

    Ah, I just saw your height in the table, I guess you are 5'8"

    2006 Norco CRR Ultegra
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    This is fantastic chaps. Thanks for yor help. I'm going to spend tomorrow arternoon visiting 4 local shops and riding as many different bikes as I can. Obviously comfort is the main thing I'm looking for and Anthony recommended ensuring the bulk of the weigh is on the saddle, but is there anything else I should be looking out to find a good fit?

    Cheers all.

    TAO

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