Reference
Bottom Bracket Identification
The most confusing system on the bike. Use this flowchart to identify what you have before buying tools or replacement parts.
The most confusing system on the bike. Use this flowchart to identify what you have before buying tools or replacement parts.
Step 1: Threaded or press-fit? #
Look at where the BB enters the frame.
- If you see threads inside the frame’s BB shell → threaded BB. Skip to Step 2.
- If the BB shell is smooth (just a round hole) and the BB is pressed into a smooth bore → press-fit. Skip to Step 3.
Step 2: Threaded BB types #
Measure the inside diameter (ID) of the BB shell threads, and check the spline pattern on the existing BB cup.
| Standard | Shell width | Thread spec | Notes |
|---|---|---|---|
| BSA / English | 68 mm road, 73 mm MTB | 1.37” × 24 TPI | Most common globally. Drive-side cup is REVERSE-threaded. |
| Italian | 70 mm | 36 mm × 24 TPI | Both sides standard-thread. Mostly older Italian road. |
| T47 | 68/86/100 mm | M47 × 1.0 mm | Modern oversize threaded standard. Both sides standard-thread. |
| PF30 to BSA adapter | Look like BSA | Same BSA threading | Press-fit shell with threaded adapter installed. |
Step 3: Press-fit BB types #
Measure the inside diameter (ID) of the BB shell, and the shell width.
| Standard | Shell ID | Shell width | Spindle |
|---|---|---|---|
| BB30 / BB30A | 42 mm | 68 mm (road) / 73 mm (MTB) / 83 mm (DH) | 30 mm |
| PF30 | 46 mm | 68 mm (road) / 73 mm (MTB) | 30 mm |
| PF30A | 46 mm | 73 mm (asymmetric — A) | 30 mm |
| BB86 / BB92 | 41 mm | 86.5 mm road / 92 mm MTB | 24 mm (Shimano) |
| PF92 | 41 mm | 92 mm | 24 mm |
| DUB Wide | 41 mm | 89/92 mm MTB | 28.99 mm DUB |
| BB386 EVO | 46 mm | 86 mm | 30 mm |
Step 4: What spindle does my crank use? #
Look at the diameter where the spindle meets the crank arm. The BB you buy must match BOTH the frame standard AND the crank spindle.
- 24 mm → Shimano Hollowtech II, FSA Mega Exo, similar
- 24/22 mm step-down → SRAM GXP
- 28.99 mm → SRAM DUB
- 30 mm → Race Face Cinch, Easton, FSA BB386, many cyclocross/road brands
- Square taper (older bikes) → cottered (rare) or cotterless square taper
Common combinations #
- “I have a Shimano Hollowtech II crank in a BSA frame” → 24 mm spindle BSA threaded BB → easy.
- “I have an SRAM DUB crank in a PF92 frame” → 28.99 mm DUB press-fit BB for PF92 shell.
- “I have a 30 mm spindle crank in a BSA frame” → need a converter BB (e.g., Wheels Manufacturing 30 mm spindle BSA threaded BB).
Replacement decisions #
- Press-fit BBs creak more than threaded. If yours creaks chronically, check whether your frame supports a threaded conversion (e.g., Wheels Mfg “Threaded Outboard” for PF30).
- Modern aftermarket suppliers (Wheels Mfg, Hambini, CeramicSpeed) make converter BBs for almost every combination.