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BB drop versus BB height(8 posts)

BB drop versus BB heightlaffeaux
Nov 21, 2003 2:16 PM
Some bike companies publish the BB drop for their frames - i.e. 7 cm - while other publish their BB height - i.e. 11.5 cm. It seems like BB drop makes more since as it never changes; BB height could vary a little based on the tire size.

What's the best way to campare these numbers? I imagine that BB height can be converted to BB drop by taking 1/2 of the wheel height (35 cm) adding some value for tires (I'd need to measure that) then subtracting the BB height. There must be an easier way...

Is there a standard values that anyone uses?
bb height is uselessgtx
Nov 21, 2003 2:42 PM
Like you said, it depends on the tire used. If it's a smaller company I'd try to call and ask for the bb drop. Probably 99% of road bikes are gonna be between 7cm and 8cm drop (with most being closer to 7), and I'm guessing that any conversion that uses an average tire height for the purpose of comparison won't yield something very accurate.
cornering clearance nmDougSloan
Nov 21, 2003 4:05 PM
A simple numberKerry Irons
Nov 21, 2003 4:28 PM
A 23mm tire/wheel has a 66.7 cm diameter. Taking half of this and subtracting the BB drop gives most everyone a BB height. Any variation in tire/wheel diameter is small relative to the total for most setups. A 20mm vs 23mm tire would only vary the BB height by 3 mm or 0.12 inches. BTW, your 11.5 cm BB height translates to 4.5 inches. What kind of bike is this? :)
opslaffeaux
Nov 21, 2003 5:40 PM
The BB height I was looking at was in inches, not cm. I love how manufactures mix units in their spec units.
oops (corrected version)laffeaux
Nov 21, 2003 5:41 PM
The BB height I was looking at was in inches, not cm. I love how manufactures mix units in their spec sheets.
what is the drop from? the axles? -nmjoe friday
Nov 22, 2003 9:03 PM
what is the drop from? the axles? ...yes...davet
Nov 23, 2003 11:48 AM
using an imaginary line, drawn from axle to axle and measured to the center of the bottom bracket = BB drop.