I recently got myself a used 2011 Specialized Demo frame. As the guy I bought the frame off and even a local bike shop were confused about the different bottom bracket options available for that frame, I’ll try to clear things up.
Specialized introduced the 2011 Demo in mid 2010. Lots of changes were made from the former model. Among these the bottom bracket shell changed to unthreaded 46mm inner-diameter and 83mm width. An article at Sicklines.com summed up the changes and the reasoning quite well.
The 2011 Demo 8 will have an 83mm bottom bracket for the first time. Specialized is also introducing the use of a press fit BB30 for the bottom bracket standard. Included with the frame will be adapters to run standard cups as well. This press fit cup system means that the Demo is somewhat future proof as when press fit 30 cranks for downhilling come about, this bike is already equipped to handle these products. Specialized is pushing the use of this bottom bracket standard with the hope to see downhill cranks made for BB30 in the near future. The main benefit will be that manufacturers will be able to make cranks with larger/stronger spindles at a lighter weight. Another benefit from the larger BB standard is there is more room at the shell to weld to making frames stronger as well as giving the consumer a potential way out that wasn’t possible before in the event of a cross threaded bb shell.
So the Demo BB is a Pressfit 30 with 83mm width. Details for Pressfit 30 can be found on the SRAM homepage at http://www.sram.com/truvativ/technologies/pressfit-30 . As found on the Specialized homepage for the Demo Frameset here a SRAM PF30 to BSA 83mm adapter is provided with the frame to allow the installation of BSA external threaded BBs.
Perfect, so let’s play this through for a Race Face Atlas FR crank with 83mm spindle length and 24mm diameter (same as Shimano Hollowtech II cranks). There are two ways to utilize that crank in the frame.
Option 1: Adapter & BSA BB
First we need to install the adapter. In my case it was already installed as you can see in the pictures. The Race Face X-Type BB is simply threaded into the adapter. The plastic sleeves provided with the BB are not needed as the adapter is a closed system and no water could enter. The cranks is then installed as usual. Don’t forget to apply some grease on the bearing races of the axle.
For details on how to install the Race Face cranks take a look at the manual here!
Option 2: Pressfit 30 – X-Type BB
Race Face offers a X-Type BB for Pressfit 30 BB shells. This let’s us avoid the adapter an install the BB directly into the frame. Nice option but I have no pictures to back this up.
Let’s switch cranks and play this through with a TRUVATIV X0 DH crankset. Be warned, as I have never owned this crankset these are unproven theories! The spec infos on the SRAM homepage are very vague, but I found some infos in different reviews and webstores. Those infos led me to believe there are three options to install the crank as it is available with different spindle diameters for 83mm width. The GXP spindle which is a tapered spindle with 24mm diameter on the drive side and 22mm diameter on the non drive side and the Pressfit 30 spindle with 30mm diameter.
Option 1: Adapter & GXP BB & GXP Spindle
As with the Race Face crankset the adapter needs to be installed first. The GXP BB is then threaded into the adapter.
Option 2: Truvativ Pressfit GXP BB & GXP Spindle
No adapter. The BB is installed directly into the BB shell.
Option 3: Truvativ PressFit 30 BB & Pressfit 30 Spindle
No adapter. The BB is installed directly into the BB shell. This would be my preferred option as it is most likely the lightest and stiffest.
Hope this was helpful for some. If you fell the need to discuss this or want to prove me wrong do so, leave a comment!