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Discussion Starter · #1 ·
Is it measured from the center of the BB or from the bottom of the shell? While perusing geometry charts, I have also come across the measurement BB Drop. Is that the distance between the center of the BB to the bottom of the shell? Thanks.
 

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Old man on a bike
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Measure bb height from bb spindle center to ground, googled for bb drop and here's Jobst Brandt's explanation: Subject: Bottom Bracket Drop
From:Jobst Brandt
Date: July 10, 2000

I'm not familiar with BB drop. How is it measured and what are its limits?

For road bicycles, using conventional sized wheels, BB drop (BB spindle centerline below wheel axle centerlines) has been empirically arrived upon at about [240mm minus crank length] for useful cornering clearance. Imbalance of pedaling in curves at greater lean causes side-slip. For this reason, higher BB's have shown no advantage in criterium racing while road races are practically unaffected by maximum cornering ability while pedaling.

Track bicycles have certain advantages on tracks with steep banking if they can ride the curves at zero speed but then that depends on track length and how it is banked.

spoke
 

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bikerboy said:
Is it measured from the center of the BB or from the bottom of the shell? While perusing geometry charts, I have also come across the measurement BB Drop. Is that the distance between the center of the BB to the bottom of the shell? Thanks.
BB drop is a framebuilders' term. When they desgn the frame on paper (or computer!) they have no way of knowing what profile of tires will be used with this bike so they can't set a BB height. So thet set a BB drop from a place they know - l line between both axle centers and it's measured to the center axis of the BB shell.
 

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Discussion Starter · #4 ·
Awesome, thank you. I figured the BB height was center to ground, but wanted to make sure. The BB drop was a new term to me, so I had just taken a wild guess at it.
 

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standards?

Follow-up question:

Are there standard BB drop measurements to which framebuilders generally adhere?

In other words, what is the "normal" range of BB drop for various bike types: mountain, 29er, road, cyclocross, and track? Anyone?
 

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Fixintogo said:
Follow-up question:
Are there standard BB drop measurements to which framebuilders generally adhere?
In other words, what is the "normal" range of BB drop for various bike types: mountain, 29er, road, cyclocross, and track? Anyone?
Here's a site with a whole load of framebuilding and spec info -

http://www.anvilbikes.com/story.php?news_ID=49&catID=3
 
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