Theory American to Mid Bottom Bracket Kit
Best conversion solution for riders updating vintage BMX frames.
This essential upgrade allows riders to install modern, high-performance three-piece cranks into older frames originally designed for American bottom brackets. By bridging the gap between legacy frame standards and contemporary bearing technology, it provides a smoother, more reliable drivetrain setup without needing to replace the entire frame.
$34.95
at
Stacked BMX Shop
Who it's for
- Vintage BMX owners looking to upgrade to modern component standards
- Daily riders seeking a low-maintenance and reliable drivetrain setup
- Custom builders prioritizing a streamlined and professional bike profile
Who should skip it
- Home mechanics lacking specialized bicycle workshop tools
- Riders planning to use oversized or heavy-duty 22mm cranksets
- Weight-conscious racers aiming for the lightest possible freestyle build
Performance breakdown
Conversion precision
Machined tolerances ensure a tight, wobble-free fit in older frames.
Bearing durability
Sealed Mid bearings handle heavy impacts better than traditional loose-ball setups.
Installation ease
Straightforward press-fit design makes upgrading vintage shells relatively painless.
Spindle versatility
Dual compatibility covers the most common modern crank spindle sizes.
Material integrity
Lightweight aluminum construction balances strength with necessary weight savings.
Rotation smoothness
High-quality bearings provide a noticeably fluid feel under heavy pedaling loads.
Key Specs
Bottom Bracket Standard
American to Mid conversion
Spindle Compatibility
19mm and 22mm
Crank Compatibility
3-piece cranks
Material
Aluminum
Sealing Type
Sealed
Serviceable Bearings
Yes
External vs Internal
Internal
Pressfit Adapter Included
Yes
Know before you buy
Still have a question?
Ask Metto anything about the Theory American to Mid Bottom Bracket Kit before you decide.
