Bottom Bracket Adapters – Solving Crankshaft Compatibility Easily
Bottom bracket adapters are specialized conversion kits that enable flexible combinations of different crankshaft standards with various bottom bracket shells. These adapter solutions create compatibility between modern crankshaft systems and existing bottom brackets without the need for costly new purchases.
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What are Crankshaft Adapters for Bottom Brackets?
Crankshaft adapters are mounted between the bottom bracket and crankshaft and compensate for different axle diameters. They make it possible, for example, to use SRAM DUB cranks with 28.99 mm shaft diameter in bottom brackets originally designed for 30 mm shafts. Conversely, 24 mm crankshafts can also be operated in larger bearings.
Common Adapter Combinations and Applications
For example, there are conversion kits for BSA 30, PF30, and PF46 bottom brackets for use with SRAM DUB shafts. These aluminum adapters make it possible to use modern DUB cranks in existing 30 mm bottom brackets without having to replace the complete bearing system.
Other adapter kits create compatibility between Thread Fit 24 and T47 24I/24X bottom brackets and various 24 mm crank systems. These high-quality adapters work with:
- 24 mm standard crankshafts
- Shimano Hollowtech II systems
- SRAM/Truvativ GXP standards
When are Bottom Bracket Adapters Useful?
System Upgrades Without Complete Replacement
Do you own high-quality bottom brackets – such as from Hope or Chris King – but want to switch to a different crankshaft technology? Then adapter kits offer a cost-effective alternative to purchasing an entirely new bearing system.
Expanding Frame Compatibility
Modern crankshaft standards continue to evolve. SRAM has introduced DUB, a unified 28.99 mm standard designed to optimally combine lightweight construction and durability. Adapters make it possible to use these new standards with older bottom brackets as well.
Flexibility in Component Selection
With the right adapters, different crank and bottom bracket combinations can be tested without having to commit to a system long-term. This is particularly valuable for:
- Testing phases of new components
- Seasonal conversions (MTB/road bike)
- Different application areas
Technical Standards and Compatibility
Important Crankshaft Diameters
- 24 mm: Shimano Hollowtech II, older standards
- 30 mm: BB30, PF30, many MTB cranks
- 28.99 mm: SRAM DUB
- GXP: SRAM/Truvativ (asymmetric 22/24 mm)
Bottom Bracket Shell Standards
- BSA: Threaded bottom brackets (68/70 mm)
- PF30/PF46: Press-fit systems for 30 mm shafts
- T47: Modern threaded standard with larger diameter
Selection and Installation
Quality Criteria
High-quality adapters from brand manufacturers such as Hope or Chris King ensure:
- Precise fit without play
- Durable materials (aluminum, stainless steel)
- Corrosion-resistant coatings
- Exact tolerances for optimal power transfer
Installation Instructions
Installation is performed similarly to normal crankshaft mounting, with the adapter functioning as an additional intermediate layer. Keep in mind:
- Use of appropriate assembly compound
- Adherence to manufacturer torque specifications
- Check chainline after installation
Limitations of Adapter Systems
Not all combinations are technically sensible or possible. Extreme diameter differences can lead to:
- Weakening of power transfer
- Chainline problems
- Increased component wear
Conclusion: Maximum Flexibility Through Adapters
Bottom bracket adapters offer an elegant solution for compatibility problems between different crankshaft and bottom bracket standards. They make it possible to continue using high-quality components while upgrading to modern standards.
We have professional adapter solutions from Hope, Chris King, and other quality manufacturers that create reliable compatibility between different drivetrain systems.