Description

BAFANG 250W Mid Drive Kit – Ebike Conversion Kit

The BAFANG 250W mid drive motor is one of the most proven, widely respected conversion units in the e-bike market — and for good reason. As the BBS01/BBS01B platform, this is a compact, precision-engineered geared mid drive motor that delivers 80Nm of maximum torque from a 250W rated power output, outperforming hub motors with three to four times its wattage on real-world terrain. The BAFANG 250W sits at the centre of your bike’s bottom bracket, uses your existing gears, and transforms a standard pedal bicycle into a highly capable, naturally-feeling electric machine. This is the mid drive ebike kit that defines what a quality e-bike conversion should be — balanced, efficient, quiet, and built to last.

Why the BAFANG 250W Mid Drive Outperforms Hub Motors

Central Placement — The Physics Advantage

The single most important advantage of the BAFANG 250W over any hub motor system is where the motor sits. Mounted at the bottom bracket — the lowest, most central point of the bicycle frame — the mid drive configuration keeps the centre of gravity low and centred between both wheels. The result is handling that feels natural and balanced rather than rear-heavy or sluggish. Cornering is sharper. Weight distribution under acceleration is more stable. The bike responds and steers like a bicycle rather than a motorised vehicle with a heavy rear wheel dragging behind it.

This geometry advantage is compounded by the fact that this e-bike conversion kit drives through the bicycle’s existing drivetrain. The motor spins the crank, the crank drives the chain, the chain runs through your existing cassette and derailleur. That means the motor benefits from every gear ratio on your bike — low gears for steep climbs, high gears for fast flat riding. A hub motor has one effective gear ratio. The BAFANG 250W has as many as your bike does.

80Nm Torque — Disproportionate Hill Climbing Power

The headline specification that separates this 250w mid drive kit from everything in the hub motor category is torque. At 80Nm maximum effective torque, the BAFANG 250W produces more rotational force at the crank than most 1000W direct-drive hub motors produce at the wheel. In practical terms, that means a 250W motor that climbs hills better, responds more immediately to pedal input, and maintains a usable power output at lower speeds where hub motors typically struggle. The geared mid drive architecture multiplies motor torque through the reduction ratio — 1:21.9 in the BBS01B — before it even reaches the chainring, producing wheel torque figures that the raw wattage rating does not suggest.

Technical Specifications

Core Motor Data — BBS01B Platform

The BAFANG 250W BBS01B is a fully specified, production-grade mid drive unit with the following confirmed specifications:

• Motor position: Mid drive (bottom bracket mounted)
• Construction: Geared brushless motor
• Nominal voltage: 36V
• Rated power: 250W
• Max effective torque: 80 Nm
• Motor RPM: 78–83 RPM (at crank)
• Reduction ratio: 1:21.9
• Efficiency: ≥80%
• Weight: 3.8 kg
• Bottom bracket compatibility: 68–73mm (JIS/BSA standard)
• Supported wheel sizes: 20–29 inch
• Noise level: <55dB
• IP rating: IPX5 (waterproof)
• E-brake support: Yes
• Throttle support: Yes
• Certifications: CE / ROHS / EN 14764
• Magnet poles: 16 (2p)
• Light output: 6V DC (up to 500mA)

Bottom Bracket Compatibility

The BAFANG 250W BBS01B is designed for bottom brackets with a shell width of 68–73mm and an internal diameter of 33.5mm — covering the JIS/BSA threaded standard used on the vast majority of road bikes, mountain bikes, hybrid frames, and city bikes. For frames with bottom bracket widths exceeding 73mm, contact us before ordering to confirm fitment. The 33.5mm axle diameter is specific to the BAFANG BBS mid drive family and is not compatible with press-fit or proprietary bottom bracket standards without adaptation.

Display Options — DZ41 or 850C

This mid drive 250w ebike kit is available with two display options depending on your build requirements. The DZ41 is a clean, functional LCD unit delivering speed, battery level, assist mode, and trip data in a compact, handlebar-mounted format. The 850C is a full-colour backlit display with a larger screen, richer data presentation, and a more premium interface — the preferred choice for builds where rider information and display quality are a priority. Both displays connect directly to the BBS01B controller with no adapter required.

Battery Options — 36V Downtube Packs

The BAFANG 250W is a 36V system, and matching battery packs are available in three capacities when ordering: 36V 15Ah, 36V 20Ah, and 36V 35Ah — all in downtube format for a clean, integrated appearance. Higher capacity means longer range per charge with no change to the motor’s performance output. For the full range of 36V compatible packs and other battery options, visit the Batteries category page.

What Makes This a Complete E-Bike Conversion Kit

Geared Motor — Efficient, Quiet, Freewheel Capable

Unlike direct drive hub motors, the BAFANG 250W uses an internal gearbox — a reduction gear set that steps the motor’s high-RPM output down to a useful crank speed. This gearing serves two critical functions. First, it allows the motor to operate within its most efficient RPM range regardless of riding speed, keeping thermal load low and energy consumption efficient. Second, it enables the motor to freewheel when not under power — the internal clutch mechanism disengages the motor from the drivetrain during unpowered riding, eliminating the drag penalty that makes direct drive hub motors exhausting to pedal without assistance. At 3.8kg, the BAFANG 250W adds minimal weight to the bicycle and that weight is positioned optimally at the bottom bracket.

Cadence PAS Sensor — Natural Pedal-Responsive Assistance

The BBS01B uses a cadence-based pedal assist sensor that detects pedalling motion and applies motor assistance proportionally. As you pedal, the motor assists. As you stop pedalling, the motor cuts out. The result is a riding experience that feels intuitive and natural — particularly effective for commuting and touring use where consistent, low-effort cruising is the priority. E-brake support is integrated, cutting motor output instantly when either brake lever is applied.

How the BAFANG 250W Sits in the Mid Drive Range

The BBS01B 250W is the entry point to the BAFANG mid drive family — the most compact, lightest, and most efficient unit in the range. For builders who need more power for heavier loads, steeper terrain, or faster riding, the Bafang Mid Drive 750W delivers triple the rated output on the same mid drive platform. For maximum performance at the top of the range, the Bafang BBSHD 1000W is the benchmark high-power mid drive unit. For the complete overview of all conversion options available, visit the Conversion Kit category page.

Specifications Summary

The BAFANG 250W BBS01B is the definitive entry-level mid drive ebike kit — compact, efficient, torque-rich, and proven across hundreds of thousands of builds worldwide. As a complete e-bike conversion kit, it transforms a standard bicycle into a properly capable electric machine without the handling compromises, maintenance demands, or mechanical drag of hub motor alternatives. This is the 250w mid drive kit that serious builders start with — and often don’t need to go beyond.

For frames with bottom bracket width more than 73mm, please contact us. Thank you!