Specialized Carbon OSBB Technical Info

Specialized OSBB is the term used by Specialized on many of their frames. Unfortunately, this doesn't tell us much about the specific dimensions of the BB shell in an OSBB frame. Most Specialized Carbon OSBB mountain frames are 73mm wide and 46mm inside diameter. This is your normal PF30 BB shell. You will use a PF30 bottom bracket that has bearings pressed into the BB cups and the cups in turn press into the frame. The exception is the Demo frames which are 83mm wide and 46mm ID.

Beginning in 2011, OSBB Carbon road frames were made with a 46mm inner diameter shell and a 61mm wide shell. OSBB Carbon road frames with a 61mm wide shell were designed to work with Specialized FACT cranks. These cranks have shorter spindles and do not fit bikes with 68mm or wider shells. If using these cranks with a Wheels Mfg PF30 bottom bracket on a 61mm wide shell, you do not need to use any additional cup spacers between the BB cups and the frame.

If you are using cranks other than the short-spindle FACT cranks on a Carbon OSBB road frame (61mm wide BB shell), you should add 3.5mm of cup spacers to each side between the cup and the frame. This effectively widens the shell to 68mm, which is what most cranks' spindle lengths are based on.

After a few years, Specialized changed their OSBB road frames by permanently bonding aluminum cups into the 61mm wide shell. The bearings are pressed into these aluminum cups. This made the frame essentially a BB30 frame (68mm x 42mm).

• Shell width: 61mm (Road), 73mm (Mountain)
• Shell ID: 46mm
• The frame's bottom bracket shell will have a smooth bore (no snap ring grooves)