Specialized bottom brackets have been confusing our customers for some time now. Many frames are carrying the OSBB label, but in reality, this Oversized Bottom Bracket covers a range of standards.

Let's run over the options and see if we can clarify it with a timeline.

Let's call everything OSBB

If my memory is correct, OSBB was first introduced on the first generation Venge, around 2011. 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.

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...'

The confusion starts because the above standard applies to carbon bikes only. 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 Specialized website consistently refers to this as 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. (Again, the Specialized website speaks of OSBB.)

The latest SL7 edition has a BSA threaded bottom bracket for both the standard and the S-Works version.

The S-works Shiv (now called Shiv-TT frame module) follows the OSBB standard as described for the Venge, but the non S-works version has an aluminum insert like the 2015 tarmac, making it BB30. (Still, Spesh calls it OSBB.)

The triathlon specific Shiv has... oh crap, who's even listening anymore. You get the picture.

How to recognize the different types of OSBB

The traditional (61x46mm) OSBB will always use a plastic insert to fit the bearings in the frame. This setup caused a lot of creaking issues. Specialized started to supply aluminum bottom bracket cups which are permanently bonded in the frame by the dealers.

  • If you see a plastic ring in your bottom bracket, that means a true to form OSBB frame. Remove the plastic cups and replace it with an aluminum bottom bracket

These plastic cups are easy to remove and can be replaced with any Kogel PF30 bottom bracket and the OSBB rings for a perfect fit.

If you see any use of aluminum in the bottom bracket shell, either because the entire frame is made of it, or because of aluminum inserts either bonded in or being part of the frame construction: your frame follows the BB30 standard. The matching Kogel collection can be found here. Just pick your crank type and you're good to go.


  • If you see any use of aluminum in the bottom bracket, your frame will follow the BB30 standard. Note that in some frames the aluminum parts will be anodized black.

But what about Specialized mountain bikes?

If you own a Specialized carbon mountain bike frame that was built in between model year 2010 to 2018, it will be following PressFit 30 standard. The Kogel collection can be found here Newer frames will be BSA threaded, but if that is not super obvious to you when you see it, I suggest you go speak to a bike shop.


2011 - 2014: OSBB was introduced on the Venge, S-Works Tarmac SL4, Roubaix and S-works Shiv. Bottom bracket shell measures 61mm wide and can be recognized by the use of plastic inserts to fit the bearings.

2015: The new Tarmac was introduced with a BB30 specific frame. In the same year Specialized started sending out warranty kits to their dealers. These kits replace the plastic OSBB inserts by permanently bonding in aluminum cups. All traditional OSBB frames come with aluminum cups from the factory. These frames now follow the BB30 standard.

If your frame is of model year 2015 or later, chances are good you will need BB30 parts to fit a crank.

2017: Specialized apparently got tired of all the press fit woes and started equipping many of their mid-level bikes with threaded bottom brackets. All the high end ones still follow the BB30 standard.

As always, I hope this makes things clearer. I probably missed a frame configuration here or there. If you have any questions regarding OSBB, feel free to connect via the 'Need Help?' button at the bottom of your screen.