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
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.
Press-Fit standards
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)
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)
BB30
The original 30 mm spindle standard, developed by Cannondale.
Dimensions:
- Shell inner diameter: 42 mm
- Width: 68 mm (road) or 73 mm (MTB)
The T47 standard
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
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 |
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.
- Check face alignment with a facing tool on new BSA and T47 frames.
- For creaking on press-fit frames: extract cups, clean the shell, apply bearing retaining adhesive, reinstall.
- When a press-fit frame chronically creaks, consider a threaded conversion kit.