AI 速览
- BSA (English threaded, 1.37" x 24 TPI, 68 mm road shell) is the most cross-compatible bottom bracket on the market — cheap, durable, and the only standard that almost never creaks
- PressFit systems (PF30, BB86, BB92) let carbon frame builders mould wider stiffer shells but are the source of most bottom-bracket creaks once the interference fit between cup and shell drifts out of tolerance
- T47 (47 mm bore, M48 x 1.0 thread) is the modern threaded answer to PressFit — a true threaded interface that fits the oversized shells PF30 created, and now the default on high-end steel and titanium
- SRAM DUB uses a 28.99 mm spindle that is not interchangeable with 24 mm Shimano Hollowtech II or 30 mm BB30 cranks — DUB is a crank standard, not a bottom bracket, and it needs the matching DUB-spec bottom bracket for whatever shell your frame has
/ 01
Why there are so many standards
A bottom bracket does one mechanical job: it lets the crank spindle rotate with minimal friction while staying rigidly located in the frame. The reason five competing standards exist is that each manufacturer solved a different problem — Shimano wanted a lighter crankset (Hollowtech II, 24 mm spindle), Cannondale wanted stiffer (BB30, 30 mm spindle in a 41 mm bore), SRAM wanted a universal crank (DUB, 28.99 mm), and frame builders wanted wider carbon shells (PF30, BB86, BB92) — and none of them agreed on a single answer.
The result is that you cannot buy a bottom bracket without knowing two things: the shell standard of your frame (which dictates the cup) and the spindle diameter of your crank (which dictates the bearing ID). Mix them up and the part either will not fit or will fit loosely and creak within a hundred kilometres.
/ 02
The four families at a glance
Shell, thread or bore, and spindle diameter for each major standard. The spindle diameter is what locks you into a crank family.
| Standard | Shell width | Interface | Typical spindle |
|---|---|---|---|
| BSA (English) | 68 mm road / 73 mm MTB | 1.37" x 24 TPI; drive-side left-hand thread | 24 mm (Shimano) |
| Italian | 70 mm | 36 mm x 24 TPI; both sides right-hand | 24 mm |
| BB30 / PF30 | 68 / 73 mm | bearings seat in 41 mm bore or 46 mm press-in cups | 30 mm |
| BB86 / BB92 | 86.5 / 92 mm | 41 mm press-fit cups in wide carbon shell | 24 mm |
| T47 | 68.5 / 73 / 85.5 mm | M48 x 1.0 threaded internal cups | 24 mm or 30 mm |
| SRAM DUB | shell-dependent | adapter-specific cups | 28.99 mm |
/ 03
Threaded: BSA and the T47 revival
BSA is the standard that refuses to die. The cups thread into the shell — drive-side reverse thread, non-drive normal — which gives a positive mechanical lock that does not depend on interference fit. BSA cups almost never creak, can be removed and reinstalled in five minutes with a 44 mm socket, and the bearings are cheap. The limitation is shell width: a 68 mm shell can only take a 24 mm spindle with room for bearings, which is why BSA cannot accept a 30 mm BB30 crank without an adapter that ruins bearing life.
T47 solves that. It is a 47 mm diameter bore threaded with M48 x 1.0 metric threads, developed by Argon 18 and Chris King in 2015 as the modern threaded answer. It fits the oversized shell openings that PF30 created but adds proper threads, accepts 30 mm spindles, and is now standard on most high-end steel and titanium frames. If you have a choice of frame and want threaded, ask for T47.
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PressFit: lighter, stiffer, creakier
PressFit bottom brackets (PF30, BB86, BB92) are held in the frame purely by the interference fit between the cup and the shell bore. There are no threads. The advantages are real: a wider shell junction lets frame builders make the bottom of the bike stiffer and lighter, and the manufacturing cost is lower because no thread machining is required.
The disadvantage is well known to anyone who has owned one. The interference fit depends on tight manufacturing tolerances on both cup and shell, and once those tolerances drift — from heat cycling, water ingress, or just a slightly out-of-spec OEM cup — the cup starts moving in the shell under pedalling load. That movement is the click-click creak on every pedal stroke. The fix is usually to remove the cups, clean both surfaces, and re-install with a retaining compound (Loctite 641 is the standard) or, on a frame that has been pressed and re-pressed too many times, to machine the shell oversize and install a repair cup.
/ 05
Lifespan and replacement
Cartridge bottom brackets are not serviceable — when the bearings feel rough or the cranks develop play, the whole unit is replaced. Lifespan depends almost entirely on conditions: a road bike ridden dry on clean tarmac may see 5,000–8,000 km from a cartridge BB; the same bike ridden through a wet winter will be lucky to see 2,000 km. Water ingress past the seal is what kills them, not load.
Cartridge BBs cost 25 to 80 USD for threaded BSA, more for PressFit and T47. Expect to replace a bottom bracket every two to four seasons on a bike ridden year-round. The replacement tool is standard-specific: a 44 mm socket for BSA and HT-II, a T47 socket for T47, and a press-fit kit for PF30/BB86/BB92. None of them are interchangeable.
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