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  1. #1
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    Cross sizing versus Road

    I have traditionally ridden a 56 road bike and am now looking at a cross bike. With the higher BB height compared to the road it seems that a 54 is the size for me. Is it normal to reduce the size 2cm when going to a cross bike? This is my first so am a newbie to it.

    Thanks...

  2. #2
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    Ride both and see whats better.
    Sometimes its a yes sometimes it's a no.

  3. #3
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    I like to go by TT length, I like a little more stand over on the cross bike, but like a similar TT length and stem length, my 2 road bikes are 58/59 CM sizes with 57 and 57.5 TT length, my cross bikes are 56CM but have 57CM top tubes and run the same 110mm stem. Some people like a slightly shorter and or higher reach on the cross bike compared to the road bike as well, but mine are set up a bit like my road bikes.

  4. #4
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    I agree top tube length is the determining factor. I prefer low BB bikes. A Specialized Crux for example has the same height as the Tarmac.

  5. #5
    jrm
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    My ML road bike (Giant Defy 1) and 55cm CX (Swobo Crosby) bike both have 56.5cm ETTs. So same ETT as your road bike only with the reach being higher since the BB is taller. Theres also compact geo's frames as well which tend to run in sm, med, lrg and xl sizing that feature shorter ST, longer ETTs and taller HTs.

  6. #6
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    Without checking the top tube length, I can say that my CAADX fits perfect with a 56cm frame. My road bikes are 58cm and also fit perfectly. I talked with the C'dale gurus at their main offices, and they indicated I should order a size down from what my roadies were - and they were right. I also rode a Surly Crosscheck and the 56cm fit was the best on that one, too. But while going down a size may be an old school rule of thumb in selecting a CX bike, it doesn't always hold true anymore - you really need to get on the bike, if possible.

  7. #7
    Clueless Bastard
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    These posters are correct. There is so much variance, you need to measure and ride each and conduct your own assessments. A cross bike is a bike I wouldn't mail order, just for these reasons.

  8. #8
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    Now that manufacturers are publishing reach and stack, I think that's the way to go.

    I've gone back and forth on whether I want to use different reach on the road vs. doing mixed surface and 'cross. Some people like 10 mm less reach. I use the same. I use less drop, though.

    So I'd look for a frame with the same reach and err on the small side. I wouldn't worry about stack unless the difference was extreme. I think if someone uses a 6° stem, going to a frame with different stack isn't that big a deal. They can always use a 17° stem if it's necessary.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  9. #9
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    I currently ride a specialized allez in a 56 and my crux is a 54. I just feel a little more in control one frame size less on the cross bike
    '14 Specialized Hard Rock Sport Disc 29
    '15 Trek Farley 6 Fat Bike
    '12 Specialized Crux Skittles
    '13 Specialized Allez

  10. #10
    z1r
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    Definitely try them on for size if at all possible.

    My Lyon is a 54.5 cm C-C with a 55.5 Top Tube C-C. My Motobecane is a size 56 but has a seat tube that measures 54 cm C-C and a top tube that measures 56 cm C-C.

    I bought a Ridley Cross Bow frame & fork this summer and after accumulating all the parts, I assembled it last weekend. Like the Motobecane it is a size 56, with a 54 cm seat tube C-C and 54.5 cm Top Tube C-C. The dimensions are almost identical to my Lyon however, the standover is a full inch higher than my Lyon. The difference being the bottom bracket drop. It is a full inch less on the Ridley. Thus, the standover is a full inch higher.

  11. #11
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    Quote Originally Posted by z1r View Post
    Definitely try them on for size if at all possible. My Lyon is a 54.5 cm C-C with a 55.5 Top Tube C-C. My Motobecane is a size 56 but has a seat tube that measures 54 cm C-C and a top tube that measures 56 cm C-C. I bought a Ridley Cross Bow frame & fork this summer and after accumulating all the parts, I assembled it last weekend. Like the Motobecane it is a size 56, with a 54 cm seat tube C-C and 54.5 cm Top Tube C-C. The dimensions are almost identical to my Lyon however, the standover is a full inch higher than my Lyon. The difference being the bottom bracket drop. It is a full inch less on the Ridley. Thus, the standover is a full inch higher.
    BB drop is not affecting your stand over. The distance from the ground to the top tube has a great effect on it though.

  12. #12
    z1r
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    Uh, yes it does. If the seat tube remains the same length but the bottom bracket height increases, so too does the standover height. The bike with the higher bottom bracket will have the top tube further from the ground.

  13. #13
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    Quote Originally Posted by z1r View Post
    Uh, yes it does. If the seat tube remains the same length but the bottom bracket height increases, so too does the standover height. The bike with the higher bottom bracket will have the top tube further from the ground.
    Stand over is not measured that way.

  14. #14
    z1r
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    Quote Originally Posted by tiretracks View Post
    The distance from the ground to the top tube has a great effect on it though.
    That's what I said. The bike with the greatest distance from the ground to the top tube has the greater standover height, right?

    So, then tell me how I was wrong? Surley seems to agree with me, "standover height (or S.O. Height"). This is the measurement from the top tube to the ground (assuming a certain tire size which is listed.) This measurement is taken at the mid-point of the top tube halfway between the seat tube and the head tube because that's where you usually end up when you stand over your frame."

    In fact, as I recall, that is the same way that most manufacturers measure it.

    Same way I measured both my bikes. Both have the same length seat tubes but the bike with the higher bottom bracket (least amount of drop) has the greater standover height.

    Now, you say I'm wrong. If so, please, explain how. Your last post was pretty scant on details.

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