Effective top tube length on a Blur LT Carbon - how to correctly measure?- Mtbr.com
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  1. #1
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    Effective top tube length on a Blur LT Carbon - how to correctly measure?

    About to pull the trigger on a large 2010 frame - SC website indicates that the top tube length should be 23.5" - I measured to 22.5" (centerline of the head tube to the centerline of the seat tube).

    The 22.5" would be a medium sized frame, but when I measured the seat tube length it was spot on for a large at 19.5"

    What did I overlook?

    Thanks!

  2. #2
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    The 23.5" inch dimension is the effective top tube measured as a straight line, parallel to ground, top center of head tube to center of seat tube ( as if extended).

    Is this how you measured?

  3. #3
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    Quote Originally Posted by enr1co
    The 23.5" inch dimension is the effective top tube measured as a straight line, parallel to ground, top center of head tube to center of seat tube ( as if extended).

    Is this how you measured?
    Yes - measured it that way. Interestingly, if I put the measuring tape at the very front of the top tube where the SC emblem is (vs. the center) it measures out to 23.5" to the center of the seat tube.

    I tried measuring it at various angles and pretty much got the same results...

  4. #4
    Don't be a sheep
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    My large measured out to exactly 23.5 using a level.
    "Do not touch the trim"

  5. #5
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    Quote Originally Posted by biketrader
    Yes - measured it that way. Interestingly, if I put the measuring tape at the very front of the top tube where the SC emblem is (vs. the center) it measures out to 23.5" to the center of the seat tube.

    I tried measuring it at various angles and pretty much got the same results...
    Interesting you say that,my large was 23.5 from the front on the steerer tube as well????

  6. #6
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    Quote Originally Posted by Rivet
    My large measured out to exactly 23.5 using a level.
    Well, I didn't use a level just a standard measuring tape...

    I called SC and the guy told me that the top tube length was difficult to measure, because it was a "virtual top tube length" and that the best way to determine the size was to measure the head tube and seat tube length...

    Interestingly, the head tube length on the large is supposed to be 4.8" but it measured 4.7"
    -I guess it must be a large...

  7. #7
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    The headtube is supposed to be 4.7". At least that's what it says on the SC website (and Speedgoat, Competitive Cyclist, etc.).

  8. #8
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    Quote Originally Posted by Wheeldog
    The headtube is supposed to be 4.7". At least that's what it says on the SC website (and Speedgoat, Competitive Cyclist, etc.).
    Hey its 3 in the morning over here

    You're right - it is supposed to be 4.7"

  9. #9
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    Quote Originally Posted by biketrader
    Hey its 3 in the morning over here

    You're right - it is supposed to be 4.7"
    It's never too early to obsess over bike geometry details. (0620 here, BTW)

    Good luck with the frame purchase.

  10. #10
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    Quote Originally Posted by biketrader
    Yes - measured it that way. Interestingly, if I put the measuring tape at the very front of the top tube where the SC emblem is (vs. the center) it measures out to 23.5" to the center of the seat tube.

    I tried measuring it at various angles and pretty much got the same results...
    Im the furthest from being a geometry/math major but there in no way the lenght dimension ("B") if measured from different angles, is going to be constant.

  11. #11
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    Since the seat tube and head tube aren't parallel, then the height (top of seat tube vs. top of head tube) that you measure at makes a difference.

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