AI 速览
- Nine out of ten 'bottom bracket creaks' are actually pedal threads, saddle clamp, or headset — isolate the source before pulling the crank.
- Shimano Hollowtech II 24mm cranks need 12-14 N·m on the left pinch bolts and 0.5-0.7 N·m on the preload cap — in that sequence.
- SRAM DUB uses a 28.99mm spindle and a 46mm ID bearing — installing standard 30mm BB30 bearings will destroy the spindle.
- PressFit BB86/92 shells should never see heavy grease in the bore — a light anti-seize film only, or the cups walk under load.
/ 01
Diagnosing the creak
Before pulling anything, isolate the creak. Stand over the bike, lock the front brake, and rock forward and backward. Creak at the pedals? Pedal threads — remove, grease to 4-5 N·m, reinstall. Creak under the saddle? Seatpost clamp or saddle rail. Only chase the BB if it creaks when you stomp on the drive-side crank with the bike in the stand.
About 90% of creaks blamed on the BB are elsewhere. Spend ten minutes isolating before removing cranks.
/ 02
Bottom bracket standards
Common bottom bracket standards and dimensions
| Standard | Shell width | Bearing ID | Spindle |
|---|---|---|---|
| BSA / English | 68 road / 73 MTB | Threaded cups | 24mm Hollowtech II |
| BB30 / PressFit 30 | 68 / 73mm | 42mm press-in | 30mm |
| PF86 / PF92 | 86.5 / 92mm | 41mm press-in | 24mm Hollowtech II |
| T47 | 68 / 85.5mm | Threaded 47mm cups | 28.99-30mm |
| BB386 EVO | 86.5mm | Press-in 46mm | 30mm |
| SRAM DUB (PF) | PF92 shell | 46mm press-in | 28.99mm |
/ 03
Tools by standard
For BSA threaded shells: a Park BBT-22 or BBT-32 (depending on notch pattern), a 1/2-inch breaker bar, and a torque wrench. For PressFit: the Park BBT-32 plus a soft-faced mallet and a press like the Park HHP-3 with PF adapters. For T47: a T47-specific socket — BSA tools won't fit. The wrong tool on a PF bearing will crack the cup.
/ 04
Threaded BSA: removal and install
Drive side = left-hand thread (tightens counter-clockwise). Non-drive = standard right-hand. Remove non-drive first, drive-side last. Clean the shell threads with a wire brush, apply a thin film of anti-seize (not grease — grease migrates and collects grit), then torque the cups to 35-50 N·m. Under-torque and the cups walk; over-torque ovalizes the shell on a thin-walled carbon frame.
Torque is a range. Lean toward 45 N·m on steel, 35 N·m on carbon, and recheck after the first few rides.
/ 05
PressFit: removal and install
Tapping out PF bearings: use a wood block on the inner race and tap alternately at 12, 3, 6, and 9 o'clock. Driving in new cups: grease the bore LIGHTLY with anti-seize, not marine grease — heavy grease hydroplanes under load. Press in until the tool bottoms out, drive-side first.
If a fresh PF cup still creaks, the bore may be out of spec — PF shells should be 41mm ID. Measure before blaming the bearings. Some frames have notoriously loose shells needing retaining compound (Loctite 609) to stay quiet.
/ 06
Crank preload and final torque
For Shimano Hollowtech II: install the right crank with the preload cap finger-tight, then tighten the left pinch bolts to 12-14 N·m in a cross pattern. THEN — the step everyone misses — back off the pinch bolts one full turn, set the preload cap to 0.5-0.7 N·m, and re-torque the pinch bolts to 12-14 N·m. Skip this and bearing preload is wrong; the crank clicks on every pedal stroke.
For SRAM DUB: single 8mm pinch bolt to 25 N·m. The NDS wave washer sets preload — replace it if compressed flat. For SRAM GXP (older 24/22mm stepped spindle), the NDS bearing is designed to slide on the spindle; don't confuse it with a Hollowtech II bearing.
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