![]() (Again, the Specialized website speaks of OSBB.) The SL6 edition of the Tarmac, introduced as a 2015 model, has a carbon frame, but with an aluminum insert, effectively making it BB30. (The Specialized website consistently refers to this as OSBB.) ![]() Aluminum bikes like the Allez and Allez Sprint are equipped with a bottom bracket shell of 68 x 42 mm, also known as BB30. The confusion starts because the above standard applies to carbon bikes only. I think the original explanation was that this was done to be able to offer a narrower Q-factor on the cranks, but I will also accept the explanation 'Just because we can.' ![]() ![]() OSBB is a narrower version of PressFit 30, sharing the same inner diameter of 46mm, but reducing the shell width to 61 versus the PF30 road standard of 68mm. If my memory is correct, OSBB was first introduced on the first generation Venge, around 2011. Let's run over the options and see if we can clarify it with a timeline. Many frames are carrying the OSBB label, but in reality, this Oversized Bottom Bracket covers a range of standards. Specialized bottom brackets have been confusing our customers for some time now.
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