Specialized OSBB bottom bracket shell (42 or 46 mm bore)
What a Specialized OSBB shell measures, which crank spindles it hosts, and the bottom bracket to buy.
Published dimensions
| Type | press fit |
|---|---|
| Shell inside diameter | 42 mm bore (alloy, BB30 style) or 46 mm bore (carbon, PF30 style) |
| Shell width | 68 mm (road) and 73 mm (MTB) |
| Thread | none on the carbon 46 mm and alloy 42 mm shells; OSBB is a Specialized name, not a separate thread |
| Crank spindles it hosts | 30 mm native; 24 mm Shimano and 28.99 mm DUB need a reducer |
SHELL 68 mm (road) and 73 mm (MTB)
SPINDLE 30 mm native; 24 mm Shimano and 28.99 mm DUB need a reducer
SPINDLE 30 mm native; 24 mm Shimano and 28.99 mm DUB need a reducer
Used on: Specialized carbon and alloy frames of the OSBB era (Tarmac SL4 to SL7, Roubaix, Venge, Shiv).
OSBB is a Specialized marketing name covering two different bores: carbon frames are a 46 mm PF30-style bore, alloy frames a 42 mm BB30-style bore. Measure the bore before buying because a 46 mm cup will not press into a 42 mm shell. Specialized moved the Tarmac, Roubaix and Aethos to BSA threaded from the SL8 generation.
Fit a crank to this shell
30 mm spindle (BB30 / PF30 style) in a Specialized OSBB shelldrops inShimano Hollowtech II (24 mm) in a Specialized OSBB shellneeds a reducerSRAM DUB (28.99 mm) in a Specialized OSBB shellneeds a reducerPF30 press fitrelated shell (46 mm bore press fit)BB30 press fitrelated shell (42 mm bore press fit)BB386EVO press fitrelated shell (46 mm bore, 86.5 mm)
SOURCES: Hambini Engineering, Specialized OSBB Engineering Guide · Kogel Bearings, Specialized OSBB explained