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  1. #1
    Raleighroader
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    How to measure stem size?

    Is it the total length of the stem, front to back, or is it only the distance from the center of the handlebar to the center of the top tube?

  2. #2
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    The nominal length of a stem is from the center of the handlebars to the center of the fork steerer.

    Usually the stem's quill bolt (threaded) or headset adjusting bolt (threadless) marks the steerer center.

  3. #3
    Raleighroader
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    Thanks. I did a brain lock when I referred to the top tube, when I meant the head tube.

  4. #4
    Senior Member acape's Avatar
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    Quote Originally Posted by HillRider
    The nominal length of a stem is from the center of the handlebars to the center of the fork steerer.

    Usually the stem's quill bolt (threaded) or headset adjusting bolt (threadless) marks the steerer center.
    I've also always been curious whether it is measured along the length of the stem (red line) or outward, perpindicular from the steerer (blue line). With a zero degree stem, these lengths will be the same, but on a stem with rise, they will be different. Maybe not much, but some.
    Attached Images Attached Images

  5. #5
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    Quote Originally Posted by acape
    I've also always been curious whether it is measured along the length of the stem (red line) or outward, perpindicular from the steerer (blue line). With a zero degree stem, these lengths will be the same, but on a stem with rise, they will be different. Maybe not much, but some.
    I've seen both quoted. I believe the more common mesurement is along the stem itself, not along a projected horizontal line.

    Unless you have a seriously up-angled stem the differences will be fairly small. Assuming a 90-degree stem and a 73-degree headtube angle, the projected horizontal distance will be 96 mm for a nominal 100 mm stem.

  6. #6
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    Quote Originally Posted by acape
    I've also always been curious whether it is measured along the length of the stem (red line) or outward, perpindicular from the steerer (blue line). With a zero degree stem, these lengths will be the same, but on a stem with rise, they will be different. Maybe not much, but some.
    I've seen both quoted. I believe the more common mesurement is along the stem itself, not along a projected horizontal line.

    Unless you have a seriously up-angled stem the differences will be fairly small. Assuming a 90-degree stem and a 73-degree headtube angle, the projected horizontal distance will be 96 mm for a nominal 100 mm stem.

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