Bafang Mid Drive Conversion Kit: Complete UK Guide (BBS01B, BBS02B & BBSHD)

The BBS01B and BBS02B require a 68mm or 73mm English-threaded (BSA) bottom bracket shell. This is the standard on the vast majority of steel, aluminium, and titanium road, hybrid, and mountain bikes sold in the UK. The BBSHD requires a 100mm BSA shell.

Press-fit (PF30, BB86, BB92) and threaded non-BSA shells (Italian, BB30) are not directly compatible — adaptors exist but add complexity and are not always ideal. If your bike has a press-fit shell, bring it in and we’ll assess whether an adaptor is appropriate for your build.

The motor unit extends toward the non-drive chainstay. You need at least 6–8mm of clearance between the BB shell face and the chainstay on the motor side. Measure before ordering — very tight frames, especially aggressive MTB geometries, occasionally fall outside this tolerance.

Bafang motors use their own chainring (supplied with the kit — typically 44T, 46T, or 48T). The chain line must align reasonably with your cassette or freewheel. For most 7–9 speed setups this works well with minimal adjustment. 10- and 11-speed drivetrains are tighter and may need more careful attention. We set chain line as part of every professional fitting.

Steel and aluminium frames are generally straightforward. Carbon frames require special care — the motor lock ring must not be over-torqued or you risk damaging the shell. We handle carbon builds at our workshop but they take longer and cost more than standard alloy frames.

You’ll need to run cables for the battery, PAS sensor, brake sensors, and display. External cable routing is simple. Internal cable routing frames need a different approach — if your frame has internal routing, bring it in for assessment before ordering, so you can plan the right cable kit.

You’ll need a crank puller and a BB removal tool matching your current BB type (cup-and-cone, cartridge, etc.). Threadlock residue on older steel frames should be cleaned out before fitting the new motor.

The motor threads into the BB shell from the drive side. Use the supplied lock ring to secure it from the non-drive side. Apply anti-seize paste on steel frames to prevent corrosion-welding over time. Tighten to the torque spec in the manual — not by feel.

Bafang supplies its own aluminium cranks and chainring. Set the chain line before fully tightening. Check chainring-to-chainstay clearance with the cranks installed at the closest point.

Downtube packs mount to the frame’s existing bottle-cage bosses (M5 at 64mm centres on most frames). Triangle packs sit inside the main frame triangle — measure your triangle carefully against the battery’s dimensions before ordering. Ensure the pack is secure and cannot rattle.

Most builds use the Bafang DPC-18 or SW102 display. Mount on the handlebars, route the cable down to the motor, and fit the PAS sensor to the bottom bracket area (the supplied magnet ring attaches to the crank spider).

Connect: motor to controller (internal), battery to controller, display cable, PAS sensor, brake sensor cut-offs (strongly recommended — they cut motor power when braking). Keep cables tidy and away from the moving drivetrain.

This is the step most DIY builders skip or get wrong. Using the Bafang USB programming cable and PC software, you can set: maximum current (and therefore power), pedal assist levels, speed cutoff, low battery cutoff, and more. For UK road use, set continuous current to deliver no more than 250W and ensure the speed cutoff is at 25 km/h. We do this as standard on every workshop build.

First power-on check: confirm display lights up, PAS responds, brake sensors cut power when levers are pulled. Short test ride to check chain tension, chain line noise, and overall feel. Check all bolts at 50 miles after initial bedding-in.

Recommended: BBS01B 250W + 48V 10–13Ah downtube battery
Quiet, lightweight, fully road-legal, and perfectly suited to city riding. The 250W version requires no programming for EAPC compliance.

Recommended: BBS02B + 48V 15Ah downtube or triangle battery
The BBS02B’s 120 Nm of torque handles sustained South Wales gradients without overheating. Programmed to 250W for road use. The 15Ah pack gives enough range for a full day without range anxiety.

Recommended: BBS02B or BBSHD + 52V 17.5Ah triangle battery
A triangle pack keeps weight centred for better handling off-road. 52V is worth the upgrade here — the BBSHD in particular benefits from the voltage headroom on sustained climbs. Aim for 850Wh+ for a full day out.

Recommended: BBSHD + 48V or 52V 20Ah triangle battery
The BBSHD’s 160 Nm of torque is the right tool for cargo loads and persistent heavy-duty use. Verify your frame has a 100mm BSA shell before ordering.

Check the label on your existing controller for its input voltage range. If the motor model is unknown, send us a photo on WhatsApp and we’ll identify it. We also offer a compatibility check and consultation at our Cardiff workshop.