Bottom bracket drop vs. BB Height- Mtbr.com
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  1. #1
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    Bottom bracket drop vs. BB Height

    What's the difference?

    How do you figure out the drop if someone gives you the height?

    Looking at three frames...2.8" Drop, 2.7" drop, 11.5" height

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  2. #2
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    Well I'm not really very smart. But drop is calculated from the centerline between the axles down to the center of the BB.

    If 2 frame have the same wheels and tires, then it should be easy enough to calculate.

    Roughing it, half of 29" is 14.5". So the 11.5" height is about 3" of BB drop.

    Sounds reasonably sound to me.

  3. #3
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    Height depends on the tires.
    Drop is a function of the frame+fork geometry.
    Like WIWR said, you have to make an assumption or know the specific dimensions of the wheels+tires to get from height to drop.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  4. #4
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    Thank you.

    The inbred is the one that listed the 11.5" height, 3" seems like a really tall bb though ?
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  5. #5
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    Quote Originally Posted by appleSSeed
    Thank you.

    The inbred is the one that listed the 11.5" height, 3" seems like a really tall bb though ?
    It actually sounds pretty low. More drop = lower BB, and 11.5" is on the low side, at least IME. It's at least 1/2" lower than all three of my 29er mountain bikes.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  6. #6
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    Ohhh, I got you. I'm dyslexic at the moment.
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  7. #7
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    11.5" sounds like a typo to me. If you got that number from Unreal's page, they list both a BB height of 11.5" and a BB drop of 58mm, but that doesn't add up. 58mm BB drop is about 12.25" BB height with an average 29er tire that is ~29.125" in diameter.

    Also, I believe that number is based on an 80mm fork, as my Inbred with 100mm fork and 2.4"+ tires has a BB height over 13.25"

  8. #8
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    How do you like it with the 100mm fork/tall BB? I've got a 100mm Fox and the other two frames (blackbuck, KM) are built around 80mm forks
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  9. #9
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    Quote Originally Posted by appleSSeed
    How do you like it with the 100mm fork/tall BB? I've got a 100mm Fox and the other two frames (blackbuck, KM) are built around 80mm forks
    I like it a lot. It tends towards the monster truck feel instead of the race car feel, but that is really only a matter of degrees (pun intended, it's really only ~1deg) and not a huge, night-and-day difference. I find it to be still nimble enough for my needs. Between the solid (if somewhat overbuilt) nature of the frame and the angles and BB height I have no worries about attacking rough trails instead of avoiding sections. The taller BB makes it really easy to avoid crank strikes on my really rocky trails.

    It certainly steers quicker and with less body english when I have my 80mm corrected rigid fork installed though.

    I'd risk trying a 120mm fork on this if it weren't for the fact that the BB height with a 100mm fork is already at the point where I would ideally like it for a 120mm fork

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