newbie question, bike size
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  1. #1

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    newbie question, bike size

    Im not too experienced with road biking but I need to buy one to start training for Track cycling in the summer. Im just wondering how this whole sizing thing works.

  2. #2

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    Quote Originally Posted by abaris
    Im not too experienced with road biking but I need to buy one to start training for Track cycling in the summer. Im just wondering how this whole sizing thing works.
    Your best bet is to go to your LBS and get sized.
    If you can't learn to do something well...Learn to enjoy doing it poorly

  3. #3
    RoadBikeReview Member
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    Online Worksheets

    Both Colorado Cyclist and Wrench Science have online worksheets to determine bike sizing. The worksheets serve more as a guide than a rule. After determining your size get out and test ride as many bikes as you have time to ride. Take notes and listen to the old guy at the bike shop. He knows more than the young whipper-snapper that is trying to sell you the $15,000 unobtanium frame, recordurace bike with wheels that defy laws of gravity.
    I don't give a damn for a man who can spell a word only one way.
    Mark Twain

  4. #4
    RoadBikeReview Member
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    Get fit

    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) 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. 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.

    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. 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.

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