????️ What it is
This is a one-piece (Ashtabula-style) crankset for 20” bikes, but it uses the smaller 43 mm bottom bracket standard, not the common 51.5 mm American size.
It’s used on:
- Some kids’ 20” bikes
- Budget BMX-style bikes
- Older or regional frame standards
???? Key specs explained
???? 20-inch bike use
- Built for BMX/kids’ geometry
- 152 mm crank arms → longer leverage than 16” versions
⚙️ 43 mm OPC bottom bracket size
This is the biggest difference:
- ✔ 43 mm = small OPC shell standard
- ✔ 51.5 mm = American (larger) OPC standard
- ❗ They are NOT interchangeable
If you fit the wrong one:
- It will not seat correctly
- Crank will bind or wobble
- Bearings will wear out quickly
???? Includes drive pin
- This version uses a retaining/drive pin system
- The pin:
- Locks crank alignment
- Helps transfer torque to the chainwheel
- Older-school OPC design compared to “W/O pin” versions
???? Steel Ashtabula construction
- One-piece forged steel crank + spindle
- Very strong, very basic, very heavy
- Built for abuse, not performance
???? Pedal threading (1/2")
- Standard BMX/kids pedal size
- Smaller than adult bikes (which use 9/16”)
???? Where it fits best
Bravvos intended this for:
- Smaller 20” bikes with 43 mm shells
- Kids’ BMX-style bicycles
- Older or budget frames using the smaller OPC standard
⚠️ Critical compatibility warning
You now have two very different 20” crank standards:
| Type |
Shell size |
Pin |
Compatibility |
| This one |
43 mm |
✔ Yes |
Smaller frames |
| Earlier one |
51.5 mm |
✖ No |
American OPC frames |
???? They are not interchangeable even if both are “20 inch” cranks
???? Bottom line
This Bravvos crank is a small-frame 20” OPC crankset with a pin-based retention system. It’s simple, strong, and cheap—but it only fits 43 mm bottom bracket frames, which is the key detail that determines everything.
