Article

🛠️ Mid-Drive on a 73mm Bottom Bracket — the Spacer Setup

Fitting a Bafang mid-drive on a 73mm shell takes two small changes: the longer fixing-plate bolts and a spacer stack. Here is the setup that clamps the motor securely.

July 12, 20262 min read

🛠️ Mid-Drive on a 73mm Bottom Bracket — the Spacer Setup

Bafang bottom bracket spacer washers used to shim a mid-drive motor on a wider 73mm shell

The Bafang mid-drive is designed around a 68mm shell but officially fits 68–73mm. On a 73mm shell (common on mountain bikes) the motor's threaded section doesn't stick out far enough for the standard hardware, so you make two changes:

  • Use the longer M6 fixing-plate bolts (~20mm) included for wider shells instead of the standard bolts — the standard ones won't reach.
  • Add a ~5mm spacer/washer stack between the fixing plate and the motor body to take up the extra width so the plate clamps flat.
  • Expect the thin outer lockring to not reach the threads. That's normal on 73mm. Secure the motor with the inner lockring torqued to ~50 Nm plus blue Loctite — that's the accepted practice and holds fine.
  • Everything else follows the standard mid-drive steps above.
If your shell measures right at 73mm and the motor still feels like it's clamping short, double-check you're using the long bolts and that the spacer is seated — this is almost always a hardware-selection issue, not a defective motor. Supplement: Bafang BBS02 750W install on a 73mm bottom bracket
Was this article helpful?

Related Articles

🛑 Brake Cutoff (E-Brake) Sensor Install

Brake cutoff sensors kill motor power the instant you squeeze a lever, the safety net that makes Bafang's cadence PAS feel predictable. Here is how to fit and test them on every build.

🛠️ Classic Pain Points (Read This If You Get Stuck)

The handful of snags that stall most Bafang installs, distilled from ten years of support calls, with the field-tested fix for each so you can get unstuck fast.

🛠️ Front-Hub Kit Install — Step by Step

The front-hub kit is the easiest Bafang install: no bottom-bracket work, you keep your cranks and shifting, and most riders are done in one to two hours. Just don't skip the torque arm.

🔦 Front LED Headlight (Optional Accessory)

The optional Bafang front LED headlight wires off the display's low-voltage output and mounts to your fork crown or handlebar. Here is how to route the lead and mount it cleanly.

⚙️ Gear Shift Sensor Install

The gear shift sensor briefly cuts motor power each time you shift so the chain moves under no load, sparing your drivetrain. Optional on the BBS02 and strongly recommended on the BBSHD.

Back to Installation