Fit Question - HeadTube/TopTube versus SeatTube
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  1. #1

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    Fit Question - HeadTube/TopTube versus SeatTube

    Hi,

    I'm deciding between a 60cm and 63cm cannondale. The problem is that I have a longer torso and arms than legs. Weird body type.

    The 60cm fits well in the seat tube; ie. the stand over height is perfect. But this frame is a little short in the top tube and the head tube is really short. which means, in order to get the right drop and total horizontal length, I'll need a lot of spacers between the headtube and the stem as well as a super long stem - 140mm plus.

    The 63 fits okay in the top tube(actually i'll still need a long stem as the top tube length is just 1cm longer) and head tube is perfect for the drop. But, this frame is a tight fit in terms of stand over height - I'll just have ~4cm of seat post sticking out.

    The fitters at the bike shop are mixed on which frame size is best. 1 guy says go larger, the other guy says go smaller and extend with a long stem with a rise.

    Any suggestions?

    I'd appreciate any input to break the tie.

    Cheers,

    Rob

  2. #2
    RoadBikeReview Member
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    Sure sounds like you need custom

    There's no question you should not be riding a bike with only 4 cm of seat post showing, especially in a frame that large. If you are going with a stock frame, go with the smaller one and get your reach and saddle-to-bar drop with a long, rising stem. Make sure that you start with the proper seat position to get you in the right position relative to the BB. If you like to ride with your knee directly over the pedal spindle (KOPS) then you'll need a longer top tube/stem than if you prefer to be farther back. Alternatively, look at other companies' geometry to find one with a longer top tube relative to the seat tube - make sure you consider the seat tube angle in this. A degree of seat tube angle moves the head tube over a cm forward or back, since your saddle stays in the same place relative to the BB. If your measurements are right, it sounds like you really need a custom frame - it costs money but it provides a bike that actually fits, and having a bike that fits is the key to an ejoyable cycling experience.

    Here's some helpful fitting information:

    Measure your inseam: stand against a wall with your feet 6 inches/15 cm apart. Push the spine of a 1 inch/2-3 cm thick book into your crotch with significant pressure, and measure the distance from the book spine to the floor. Your saddle top to pedal axle should be 108-110% of the inseam measurement.

    Here are several frame fit calculators.

    http://www.bsn.com/cycling/ergobike.html
    http://www.coloradocyclist.com/BikeFit/index.cfm
    http://www.sheldonbrown.com/harart-frames.html
    http://www.rivendellbicycles.com/fra...ame_Sizing.htm
    http://www.peterwhitecycles.com/fitting.htm

    For adjusting the fit of the bike, there are roughly five starting points:
    1. Seat height (top of saddle to center of pedal axle) at 108-110% of inseam.
    2. Saddle parallel to ground.
    3. Saddle fore/aft adjusted so that a plumb bob from the bony protrusion just below the kneecap passes through the pedal axle when the cranks are horizontal. This is known as KOPS (Knee Over Pedal Spindle). To measure your knee over pedal spindle (KOPS) situation, drop a plumb line from the front of the bony protrusion just below the knee cap.
    4. Front hub axle obscured by the handlebars when riding in your "regular" position (drops, hoods, or tops).
    5. Top of handlebars 1 to 4.5+ inches below the top of the saddle depending on your flexibility and size.

    These are all starting points for "average" proportioned people, and many folks like to move away from these starting points as they learn what makes them more comfortable, powerful, or efficient. For example, the KOPS position range is typically +1 to -2 cm, depending both on your personal physiology (long femurs tend to push the saddle back) and pedaling style (spinners move the saddle forward, pushers move the saddle back). You want to get the fit of the frame as close as you can, then do minor adjustments with the stem, seat post, saddle position, etc.

    A lot of this is personal comfort, and we all tend to adapt to a given position over time. For example, a given stem length may be right for you, but it may feel long at first. I use the "handle bar obscures the front hub" rule for my fit, but others claim better position (for them) with the hub in front of or behind the bar. I'm 6' tall and ride with 11.5 cm drop from saddle to bar, probably more than most people would like but fine for me. Some are suggesting zero drop from saddle to bars - it's about comfort, efficiency, and aerodynamics. The ERGOBIKE calculator is pretty good, but it is not infallible. I would suggest riding some miles (over 100 total, and over 500 would be better) and see if you adapt to the position. There are no hard and fast rules, just general guidelines, when it comes to these things.

    Just as important as your size is your flexibility. If you have a stiff lower back, you may not be able to lean over and stretch out as much. If you are very flexible, you may get away with a longer top tube, with the stem in a lower position. Over time on the bike, too, you may become more limber, or at least become accustomed to being lower and stretched out. So, your first 'real' bike may not be anything like what you will want 5 years from now.

    Someone new to road riding is highly unlikely to find their ultimate position on the first go. As they become accustomed to the riding position and get some miles in, sometimes over several seasons, people often find their desired position changing. What was "stretched out" now feels OK, or what was "just right" now feels cramped. With time, if you are working on your position along with all your other riding stuff, seat position tends to rise, handlebars tend to be farther below the saddle, saddles tend to move rearward, and handlebars tend to be farther forward from the saddle. You simply cannot say "this is the right position for someone of your body dimensions" because there are too many variables and things that change with time. Get used to your position, and then occasionally make small changes: raise/lower your saddle, move your saddle forward/backward. Ride a while with the changes (a few 100 miles, anyway) and decide if it is better or worse. If it is better, keep moving in that direction. If it is worse, try moving the other direction. If you don't try, you won't find out, but it is a long term process, often taking years, to really dial in your position. And since your strength and flexibility are changing with time, it is reasonable that your position would need to change also.

  3. #3
    RoadBikeReview Member
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    neither one??

    Why buy a frame that doesn't fit? Obviously both have significant drawbacks. You should consider a custom to get the "perfect" dimensions, or at least look into sloping TT frames that would increase your standover clearance. For example, Giant's TCR comes in an XL size that has a 61cm TT length wiht a 73 degree STA, but they don't advertise the head tube length. The Giant XL has the longest top tube I could find.

    The only thing that doesn't make sense to me is the need for a long head tube. If you have short legs and a low saddle height, the saddle to bar height difference should not be that great on the smaller frame. With a long torso (and long arms?) you should be able to handle an 8-10 cm height difference. If you can't then it seems like you want a touring bike fit, but you're looking at racing frames.

    You also quote the need for a 140+ stem on the 60cm frame, but the TT on the 63cm is only 1cm longer, which is not a huge improvement. Seems like both are too short in the top tube.

    Also, if your saddle is positioned to place your knee directly over the pedal spindle, moving the saddle back 2cm and down .6cm could solve your fit problem without compromising pedaling efficiency.
    Last edited by C-40; 09-08-2004 at 12:41 PM.

  4. #4
    RoadBikeReview Member
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    Neither. Look at some other bikes. Maybe a compact style frame will solve the standover issue if you want to stay with off-the-rack bikes.

  5. #5
    RoadBikeReview Member
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    True. Definitely go compact.

    Maybe look at specialized. THey have more size options than Giant.

    Quote Originally Posted by Henry Chinaski
    Neither. Look at some other bikes. Maybe a compact style frame will solve the standover issue if you want to stay with off-the-rack bikes.

  6. #6
    RoadBikeReview Member
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    Smaller

    Well, it's the logical choice dude. If you really love the frame, and don't want anything else, you can only go for the smaller frame with a longer stem and a setback post. That's because if you go for the larger frame, you can't stand over it.

  7. #7

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    I would suggest you follow the other peoples advice and find a different frame. If you really want to have the cannondale, no brainer, get the larger frame. You don't stand over the bike, you ride it, and if it doesn't fit when you are riding, nothing else matters.

  8. #8
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    sorry

    I have to disagreed because ultimately you have to stop...

  9. #9

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    My point was, nothing matters if the bike doesn't fit when you are on it. You can deal with a bike that has to high of a standover by keeping one foot clipped in when you stop to get extra clearance when you stop (trust me it works, used to do it all the time when I was a kid). The real answer as others have said, is that this is obviously not the right frame for this guy and he needs to find something different

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