A Specialized Tarmac SL6 (2018 to 2020) frame uses a Specialized OSBB bottom bracket shell (42 or 46 mm bore). The dimensions, which cranks fit, and the exact bottom bracket to buy.
Updated 05 September 2026.
What bottom bracket does a Specialized Tarmac SL6 (2018 to 2020) use?
The bottom bracket shell standard on a Specialized Tarmac SL6 (2018 to 2020), and how to pick the right BB.
| Frame | Specialized Tarmac SL6 (2018 to 2020) |
|---|---|
| Shell standard | Specialized OSBB (42 or 46 mm bore) |
| 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) |
SPINDLE see table
The Specialized Tarmac SL6 (2018 to 2020) uses a Specialized OSBB bottom bracket shell (42 or 46 mm bore), a 42 mm bore (alloy, BB30 style) or 46 mm bore (carbon, PF30 style), 68 mm (road) and 73 mm (MTB) wide.
It is a press-fit shell, so bearings or cups press into the 42 mm bore (alloy, BB30 style) or 46 mm bore (carbon, PF30 style). Match the shell width as well as the bore, because a shorter unit will not preload the crank across a wider shell.
SOURCES: Hambini Engineering, Specialized OSBB Engineering Guide · Cycling Weekly, Road bike bottom bracket standards explained · Kogel Bearings, Specialized OSBB explained
Questions and answers
What bottom bracket does a Specialized Tarmac SL6 (2018 to 2020) use?
A Specialized Tarmac SL6 (2018 to 2020) frame uses a Specialized OSBB bottom bracket shell (42 or 46 mm bore).