Wednesday, 19 March 2008 17:47
|Bottom Bracket Types|
...Bottom Bracket Types, Continued
Page 1 - External Thread-In Bottom Brackets (Hollowtech II, GXP, X-Type...)
Page 2 - Internal Bottom Brackets (square taper, Octalink, ISIS...)
Page 3 - Internal Press-In Bottom Brackets (BB30, BB86, BB92...)
Internal Press-In Bottom Brackets:
Bearings Pressed Inside of Bottom Bracket Shell
All of the previously mentioned bottom brackets house bearings in a cup or shell which is then screwed into the shell of the frame. The newest style of bottom brackets dispense of that threaded bearing cup and have the bearings pressed directly into the frame, sometimes without a cup of any sort. There are many excellent reviews and discussions out there on the old inter-webs about the pluses and minuses of the different systems (eg, stiffness, q-factor, compatibility) and their origins but I plan to keep it real simple here.
BB30 - Shop For Them Here
The '30' in BB30 refers to the diameter of the crank spindle.
Bearing with a 42mm outside diameter (OD) and a 30mm inside diameter (ID) drop directly into compatible frame shell. A c-clip creates a shelf that the bearing sits up against. Crank uses 30mm spindle. BB30 frames can utilize either a 68 or 73mm width shell, generally road or mountain, respectively.
At the time of writing there is no Shimano crank that is BB30 compatible nor will there be anytime soon. However, BB30 bottom brackets can be adapted to accept some non-BB30 cranks, for example, Shimano Hollowtech II or TruVativ GXP. See some adapters HERE. Other adaptations may be available, call us for your specific questions or needs.
PressFit30 (PFBB30) -
Same as BB30 above except the bearings are housed in a cup that is pressed into the frame. PressFit30 frame bottom bracket shells have a larger ID than BB30 in order to accept the larger bearing/cup. PressFit 30 frame bottom bracket shell ID (or the bearing's OD) is 46mm vs 42mm on a BB30 frame.
PressFit 30 systems use the same crank as BB30.
There are adapters to convert PressFit 30 frame shells to accept non-BB30 cranks, call us for current options depending on your needs.
BB86/BB91 - Shop For Them Here
The number in BB86 or BB91 refers to the shell width of the frame, generally road and mountain, respectively. This standard was introduced by Shimano and involve bearings pressed into cups that are pressed into the frame. These utilize cranks with 24mm bottom bracket spindles and use the same bearing OD/ID dimensions as are found in external cup bottom brackets (Hollowtech II, MegaExo).
It might help to think of it this way - When you take a traditional 68 or 73mm threaded bottom bracket shell and thread in external bearing cups (Like Shimano HollowTech,
This system is used by Trek and is similar in design to the BB86/91 systems above but there is no bearing cup, the bearing sets directly into the frame. Uses crank with 24mm spindle.
BB386 EVO -
A system designed by BH Bikes collaboration with FSA. This system uses a very similar bearing and cup as PressFit 30 but it is placed the same width as the BB86 system. The system is intended for road only because of the large size of the cup needed to fit the bearing and the wide width it is placed at (the large width and diameter of BB386 EVO on a mountain bike could interfere with using a granny gear and could interfere with pivot placements on full suspension bikes).