Bottom Bracket Drop by Jobst Brandt

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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 [240 mm 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.

Jobst Brandt

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