BB drop vs BB height : Rocky Mountain bikes


Turbo Monkey
Sep 24, 2001
I did a search but found nothing...

I'm confused concerning the BB drop measurement. According to this image, the BB drop is the distance F:

If I understand correctly, the BB drop is the distance between the BB and an imaginary line connecting the front and rear axles...so a BB drop = 0 means a BB at the same height as the axles (let's say 13"), a BB drop of 1", means a 12" BB height, etc.

When I look on the Rocky Mountain website the
Element: 20mm BB drop
ETS-X: 20mm
Slayer: 16 mm
Switch: 36 mm
Vertex: 30 mm (!)

I'm confused... It could make sense if these numbers refered to the distance above the line connecting the axle...but it would imply a BB height over 14" for the Vertex.

My guess would be that there is a minus sign that is missing for the BB drop of the FS bike, indicating that the BB height is above the line connecting the axles. That would make sense...but why would they put a lower BB on the Slayer than on the Element?

Actually, all this thinking is useless...I want to know the BB height of the ETS-X. :p ;)
Is it ~13"+20mm ~ 13.8" ?


binary visions

The voice of reason
Jun 13, 2002
Um, they don't have a real BB height measurement? All they list is the drop?

There are definitely some issues with that BB drop measurement. There's no way the RM Switch has a ~12.5" (~13"-36mm) BB height.

I would contact Rocky Mountain and ask them. Strictly speaking (that is, according to what the BB drop technically means, and what they have listed on the website), the ETS-X will have a ~13"-20mm = ~12.25" BB height.


Jul 15, 2005
At a computer...duh
Wow....that's just retarded.

1) You're correct, those #'s don't make a bit of sense.
2) That is the only company to give their BB measurements like that. Nobody keeps in mind the exact height of the rear axle with the tire mounted.


Turbo Monkey
Sep 24, 2001
I went to my lbs to measure the BB height of a real ETS-X. It was around 13.8", which seems to confirm that there's a minus sign missing for the BB drop of the FS bike, but the bb drop listed for the hardtails makes sense.

Congrats to the genious at RM who managed to screw this up! :rolleyes: :help: