⚙️ Gear Shift Sensor Install
The gear (shift) sensor sits inline on your derailleur cable and detects when you shift. When it sees cable movement it tells the controller to cut motor power for about 0.8 seconds so the chain shifts under no load. That single feature dramatically reduces chain and cassette wear and prevents the "clunk" of shifting under full motor power. It's optional on BBS02, strongly recommended on BBSHD.
- Find a cable spot with slack. Pick a straight section of exposed derailleur cable and housing with a little room — commonly along the top tube or chainstay run.
- Cut the cable housing to insert the sensor. The sensor bridges a gap in the housing (not the bare inner cable). Cut the housing where the sensor will sit, following the length in the Bafang gear sensor manual. Measure twice — you want the two housing ends to seat fully into each end of the sensor with the inner cable running straight through.
- Route the inner cable through the sensor and re-seat both housing ends into the sensor body. The inner cable must slide freely.
- Re-tension and re-index the derailleur. Because you shortened the housing run, re-set the cable tension and index the gears exactly as you would after a normal cable change, so every gear shifts cleanly.
- Connect the sensor's Higo plug into the gear-sensor lead on the harness (arrows aligned).
- Test. Power on and shift up and down while pedaling gently (wheel off the ground) — you should feel/hear the motor briefly pause on each shift.