[crashing_sux]

I was curious about the BB height on the new RMX so I went to the Rocky Mountain website to look at the geometry specs but instead of listing BB height like most manufacturers do they only list BB drop = 7.

What is BB drop and can it be used to determine BB height?

 

[buildyourown]

BB drop is the distance from the axle line to the BB. This is a carry over from road bikes which have a lot of drop. This is more accurate since BB height will change with tire and wheel choice. So, to calculate BB height, measure your axle height and subtract drop. 7" sounds like way too much. It might be 7mm.

 

[crashing_sux]

Axle height is going to be around 13.5", anything lower than that sounds way to low for a bike with 8" of travel, and I remember hearing somewhere that the RMX had a tall bottom bracket, which would definitely be over 13.5".

 

[Shortbus]

i think by axle height he meant rear wheel axle (QR) height.

My bike has negative BB drop, i.e. the BB sits higher than my rr wheel's axle.

EDIT: you know i achully think am completely off. try this:

http://www.sheldonbrown.com/bbdrop.html

 

[Shortbus]

achully , here you/I go, according to gary fisher:

BBD ( mm ) bottom bracket drop
The vertical distance the bottom bracket is below an imaginary horizontal line drawn through the axles. The greater the bottom bracket drop, the lower the rider’s center of gravity.

I'm again assuming he's talking about the wheel axles, which is not necesarily a perfect horizontal line! (think 26 front 24 rear setup).

 

[crashing_sux]

That sounds like it still puts the RMX BB height at around 13.5". I'm not that concerned that I need to keep digging into it but that just sounds wrong to me.