Triathlon / TT Bike Bottom Brackets

Measure the shell width on your frame: common triathlon shells are 68mm for road/TT and 73–100mm for wider TT setups. Matching that width helps you pick the right standard—68mm shells often use BB30/PF30, while MTB-influenced 91.5mm options like the FSA BB392EVO suit wider builds.

For stiffness-to-weight, 30mm spindles (BB30) typically deliver a stiffer feel than 24mm Shimano/SRAM spindles because of the larger spindle and bearing sizes. If your crankset is 24mm you’ll want a shell or adapter that accepts that diameter to avoid misalignment in aggressive TT geometry.

T47 is a good choice when you want threaded reliability and reduced creak for high-torque TT efforts; it uses M47x1 threading and a 46mm ID to accommodate oversized bearings. Chris King T47 examples show how the larger threaded interface improves longevity and sealing compared with some press-fit shells under vibration.

BBright’s asymmetric 45/34mm layout shifts the bearing center to improve chainstay clearance and lateral stiffness on Cervelo S Series bikes, and its 79mm asymmetric width helps optimize aero-focused frames. That asymmetric stiffness is useful in windy, high-speed efforts where lateral rigidity and chainline matter.

Yes, adapters exist to convert BB30/PF30 shells to different spindle sizes, but you must match shell diameter (46mm press-fit or 34.8mm BSA) and check chainset compatibility. Verifying those dimensions prevents misalignment and potential creaks when fitting a 24mm crank into a 30mm shell.