[Leon94]

I was wandering if there was a standard BB length for mountain bike frames regardless of the frame's actual BB width. I have four different mtb frames and noticed they all had slightly different widths at the bottom bracket area ranging between 2.6" and 2.9" wide while I was deciding on what to buy for one of the frames.

I am pretty sure it takes a BB with a length longer than the traditional 113mm. If you're installing a 113mm BB with the fixed side on the drive side, I would imagine the non-drive side where the pedal is installed might be too close to the chainstay.

-----------------------------------------

Having the correct chain line is critical to a smooth and dependable drive train. Different frames use specific type of BB (american, Euro, etc.) and BB shell, and that BB length depends on the exact crank set used.

In addition to having a correct chain line and drive train, installation is just as important. Many riders complain about their awful bottom bracket, when in reality they either failed to follow the directions properly or may not have used the right tools. Many people also refuse to use a torque wrench to set the proper torque.

I would be more confident as a rider knowing all 26 components were installed correctly.

 

[BikeSATORI]

I was wandering if there was a standard BB length for mountain bike frames regardless of the frame's actual BB width. I have four different mtb frames and noticed they all had slightly different widths at the bottom bracket area ranging between 2.6" and 2.9" wide while I was deciding on what to buy for one of the frames.

I am pretty sure it takes a BB with a length longer than the traditional 113mm. If you're installing a 113mm BB with the fixed side on the drive side, I would imagine the non-drive side where the pedal is installed might be too close to the chainstay.

-----------------------------------------

Having the correct chain line is critical to a smooth and dependable drive train. Different frames use specific type of BB (american, Euro, etc.) and BB shell, and that BB length depends on the exact crank set used.

In addition to having a correct chain line and drive train, installation is just as important. Many riders complain about their awful bottom bracket, when in reality they either failed to follow the directions properly or may not have used the right tools. Many people also refuse to use a torque wrench to set the proper torque.

I would be more confident as a rider knowing all 26 components were installed correctly.

no, not really a standard... of course, there are "MTB" standards, but no standard measurement that is guaranteed to fit all bb's of a specific size. Like you said, it depends highly on chainstay clearance, as well as other factors like tire width, suspension design (if it exists), rear hub spacing or offset, etc, etc.
Typical "mtb" cartridge bottom brackets highly differ from bmx style bb's with a floating spindle, the spindle on an mtb cartridge is fixed inside the unit as one piece and cannot be moved. Chainline is usually not a problem at all with bmx bb's since they are essentially infinitely adjustable within it's length.