Why so many standards?
The bottom bracket (BB) is the interface between the crankset and the bicycle frame. It's a critical component that bears the full force of pedaling. Over the decades, frame and groupset manufacturers have multiplied standards to gain stiffness, save weight, or simply to differentiate themselves. The result: a jungle of standards that makes crankset/frame compatibility sometimes confusing.
Understanding these standards is essential for every bike mechanic. A standard mismatch can lead to a bottom bracket that won't fit the frame, a crankset spinning on an undersized spindle, or creaking noises impossible to eliminate.
Threaded standards
BSA (British Standard)
BSA is the oldest and most widespread standard. The bottom bracket threads into the frame with a 1.370" x 24 TPI thread (approximately 34.8 mm). The drive-side cup threads in reverse (left-hand thread) to prevent loosening from pedaling.
Dimensions:
- Thread diameter: 1.370" (34.8 mm)
- Shell width: 68 mm (road) or 73 mm (MTB)
- Thread pitch: 24 TPI
Advantages:
- Universal standard, enormous choice of bottom brackets and cranksets
- Easy to install and remove
- Repairable: threads can be re-tapped if damaged
- No creaking if properly installed with thread grease
Disadvantages:
- Wider manufacturing tolerances than press-fit
- Slight theoretical stiffness loss (thread material takes up space)
Compatible cranksets: Shimano Hollowtech II, SRAM GXP, SRAM DUB, Campagnolo Ultra-Torque, FSA MegaExo, Race Face Cinch. Virtually all cranksets come in a BSA version.
Italian
Less common today, the Italian standard features a larger thread (36 mm x 24 TPI) and notably both sides thread in the same direction (right-hand thread). Shell width is 70 mm.
Found mainly on vintage Italian frames (Colnago, vintage Pinarello, De Rosa). Some track frames still use it.
Press-Fit standards
Press-Fit was introduced to allow wider, stiffer bottom bracket shells without threading. Bearings are pressed into the frame via plastic or aluminum cups.
BB86 / BB92 (Shimano Press-Fit)
Developed by Shimano, this is the most widespread press-fit standard in high-end bikes.
Dimensions:
- Shell inner diameter: 41 mm
- Width: 86.5 mm (road, hence BB86) or 89.5/92 mm (MTB, hence BB92)
- Crankset spindle: 24 mm (Shimano, FSA) or 28.99 mm (SRAM DUB)
Advantages:
- Wider shell = stiffer frame at the critical zone
- Quick installation
- Compatible with many cranksets via adapters
Disadvantages:
- Cups can develop play in the frame (creaking)
- Requires dedicated press and extraction tools
- Sensitive to frame machining precision
Compatible cranksets: Shimano Hollowtech II (native), SRAM GXP (via adapter), SRAM DUB (via 28.99 mm adapter), Campagnolo Ultra-Torque (via adapter).
PF30 (Press-Fit 30)
Introduced by SRAM for its 30 mm spindle.
Dimensions:
- Shell inner diameter: 46 mm
- Width: 68 mm (road) or 73 mm (MTB)
- Crankset spindle: 30 mm
Advantages:
- 30 mm spindle = very stiff and lightweight
- Even wider shell than BB86
Disadvantages:
- Same creaking issues as all press-fit
- More limited crankset choice (30 mm native spindle)
- Requires adapter for 24 mm cranksets (Shimano)
BB30
The original 30 mm spindle standard, developed by Cannondale.
Dimensions:
- Shell inner diameter: 42 mm
- Width: 68 mm (road) or 73 mm (MTB)
- Spindle: 30 mm
- Bearings mounted directly in frame (no cups)
Advantages:
- Minimal weight (no intermediate cups)
- Very stiff
Disadvantages:
- Extremely critical frame machining tolerances
- Chronic creaking if frame isn't perfectly machined
- Delicate bearing replacement
- Declining standard (even Cannondale has moved on)
The T47 standard
The answer to press-fit problems
T47 was developed by Chris King and Argonaut to combine press-fit advantages (wide shell) with threading benefits (no creaking).
Dimensions:
- Thread diameter: 47 mm x 1 mm (metric)
- Width: 68 mm (road) or 85.5 mm (MTB)
- Compatible with 24 mm, 28.99 mm (DUB), and 30 mm spindles
Advantages:
- Threaded = no creaking, easy install/removal
- Large diameter = stiff frame
- Compatible with all major spindle standards via different BB cups
- Open standard, no proprietary license
- Growing adoption (Specialized, Trek, Santa Cruz, Cervelo...)
Disadvantages:
- Newer, so less cup choice than BSA
- Requires specific tool (T47 wrench)
- Older frames not compatible (retrofit impossible)
Comparison table
| Standard | Type | Shell dia. | Width | Compatible spindles | Creaking? |
|---|---|---|---|---|---|
| BSA | Threaded | 34.8 mm | 68/73 mm | 24, 28.99, 30 mm | Rare |
| Italian | Threaded | 36 mm | 70 mm | 24 mm | Rare |
| BB86/92 | Press-Fit | 41 mm | 86.5/92 mm | 24, 28.99 mm | Frequent |
| PF30 | Press-Fit | 46 mm | 68/73 mm | 30 mm (native) | Frequent |
| BB30 | Press-Fit | 42 mm | 68/73 mm | 30 mm | Very frequent |
| T47 | Threaded | 47 mm | 68/85.5 mm | 24, 28.99, 30 mm | Rare |
Which crankset on which standard?
The most common workshop question is: "Will this crankset fit my frame?" The answer depends on two factors: the frame standard and the crankset spindle diameter.
Shimano Hollowtech II (24 mm spindle):
- BSA: SM-BBR60 or SM-BB72-41B cup
- BB86: SM-BB72-41B (press-fit)
- PF30: PF30 to 24 mm reduction adapter
- T47: T47 cup for 24 mm spindle (Chris King, Wheels Manufacturing)
SRAM DUB (28.99 mm spindle):
- BSA: DUB BSA cup
- BB86/92: DUB PressFit cup
- PF30: DUB PressFit 30 cup
- T47: DUB T47 cup
Practical workshop tips
- Always identify the frame standard before ordering a bottom bracket. Measure the shell inner diameter and width.
- Grease BSA and T47 threads during installation. Use anti-seize paste on press-fit cups.
- Use a dedicated press tool for press-fit. Never hammer cups in, even with a guide tube.
- Check face alignment with a facing tool on new BSA and T47 frames. Misalignment causes premature bearing wear.
- For creaking on press-fit frames: extract cups, clean the shell, apply bearing retaining adhesive (Loctite 641 or equivalent), reinstall.
- When a press-fit frame chronically creaks, consider a threaded conversion kit (Wheels Manufacturing PressFit-to-threaded). This creates a BSA thread inside the press-fit shell and permanently eliminates creaking.