Bafang Mid Drive Conversion Kit: Complete UK Guide (BBS01B, BBS02B & BBSHD)
In this article
- What is a Bafang Mid Drive Motor?
- BBS01B vs BBS02B vs BBSHD — Which Is Right for You?
- UK Law and the 250W EAPC Rule
- Frame Compatibility: What to Check Before You Buy
- Installation Overview
- Choosing the Right Battery
- DIY vs Professional Fitting — The Honest Answer
- Which Motor for Your Use Case?
- Get Your Bafang Fitted in Cardiff
- FAQ
Short answer
For most UK riders converting a standard bike, the BBS02B at 48V is the sweet spot for hilly roads. It can be programmed to the 250W EAPC limit and pedal-assist-only operation, with a 25 km/h cutoff. Check the bottom bracket shell (68mm or 73mm BSA for the BBS01B and BBS02B) and the battery before choosing the motor.
What is a Bafang Mid Drive Motor?
A mid drive motor mounts in your bike’s bottom bracket shell — the threaded housing at the base of the frame where the cranks and pedals attach. Unlike a hub motor, a mid drive sends power through the bike’s existing chain and gears, meaning the motor benefits from your cassette on steep hills.
Want to understand the full mid drive vs hub motor debate? We’ve written a technical side-by-side in our rear hub motor vs mid drive comparison guide.
BBS01B vs BBS02B vs BBSHD — Which Is Right for You?
| Motor | Rated power | Peak torque | BB shell size | Best for | UK road legal? |
|---|---|---|---|---|---|
| BBS01B | 250W / 350W | ~80 Nm | 68mm / 73mm BSA | City commuting, lighter riders, legal builds | Yes (250W version) |
| BBS02B | 750W (programmable) | ~120 Nm | 68mm / 73mm BSA | Hilly commutes, heavier riders, trail use | With correct programming |
| BBSHD | 1000W (programmable) | ~160 Nm | 100mm BSA | Off-road, cargo, e-MTB, demanding builds | When programmed |
UK Law and the 250W EAPC Rule
In the UK, an eBike is legally classed as an Electrically Assisted Pedal Cycle (EAPC) and can be ridden on public roads without registration, insurance, tax, or a driving licence — provided it meets all three conditions:
| Condition | Requirement | What it means in practice |
|---|---|---|
| Motor power | No more than 250W continuous | Higher-wattage motors can comply if programmed to limit continuous output to 250W. |
| Assist type | Pedal assist only | The motor must only run while you’re pedalling. |
| Speed cutoff | Assist must stop above 15.5 mph (25 km/h) | The controller must cut power at this speed. |
Key point: A BBS02B rated at 750W can be programmed to deliver 250W-limited, pedal-assist-only output — and when configured correctly, it is road-legal. We configure every road-use build to EAPC spec at our Cardiff workshop before handover.
Frame Compatibility: What to Check Before You Buy
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Bottom bracket shell size and thread
The BBS01B and BBS02B require a 68mm or 73mm English-threaded (BSA) bottom bracket shell. The BBSHD requires a 100mm BSA shell. Press-fit shells (PF30, BB86, BB92) are not directly compatible.
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Chainstay clearance
You need at least 6–8mm of clearance between the BB shell face and the chainstay on the motor side.
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Chain line
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.
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Frame material
Carbon frames require special care — the motor lock ring must not be over-torqued or you risk damaging the shell.
Shell width is only part of the picture, so work through our full Bafang compatibility check before you order.
Installation Overview
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Remove the existing crankset and bottom bracket
You’ll need a crank puller and a BB removal tool matching your current BB type.
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Thread in the Bafang motor unit
The motor threads into the BB shell from the drive side. Use anti-seize paste on steel frames. Tighten to the torque spec in the manual — not by feel.
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Fit the chainring, cranks, and battery
Set the chain line before fully tightening. Downtube packs mount to the frame’s existing bottle-cage bosses.
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Run and connect all cables
Connect: battery, display, PAS sensor, brake sensor cut-offs. Keep cables tidy and away from the moving drivetrain.
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Program the controller
Using the Bafang USB programming cable and PC software, set the speed cutoff to 25 km/h and continuous current to deliver no more than 250W for UK road use.
Fitting the biggest motor in the range? Our BBSHD installation guide goes through that build step by step.
Choosing the Right Battery
| Motor | Recommended voltage | Minimum capacity | Typical range |
|---|---|---|---|
| BBS01B 250W | 36V or 48V | 10Ah (360–480Wh) | 25–45 miles |
| BBS02B 750W | 48V (52V for more performance) | 13Ah (624Wh) | 30–55 miles |
| BBSHD 1000W | 48V or 52V | 17.5Ah (840Wh+) | 35–60 miles |
Downtube battery
Mounts to bottle-cage bosses on the downtube. Easy to remove for indoor charging. Browse batteries →
Triangle battery
Sits inside the main frame triangle. Better weight distribution, higher capacity options, and a cleaner look.
DIY vs Professional Fitting — The Honest Answer
When to DIY
- You have a standard 68mm BSA frame with external cable routing
- You’re comfortable with bicycle tools and have done BB work before
- You have time to research and troubleshoot the programming step
When to use a workshop
- You want the motor correctly programmed for UK road legality
- Your frame is carbon, has internal cable routing, or a non-standard BB shell
- You’re fitting a BBSHD — the larger motor demands more experience
- You rely on the bike daily and can’t afford downtime from a mistake
Which Motor for Your Use Case?
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Daily commuter, flat to moderate terrain
Recommended: BBS01B 250W + 48V 10–13Ah downtube battery. Quiet, lightweight, fully road-legal.
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Hilly commute — South Wales terrain, heavier rider
Recommended: BBS02B + 48V 15Ah battery. Handles sustained South Wales gradients without overheating.
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Trail riding and off-road e-MTB conversion
Recommended: BBS02B or BBSHD + 52V 17.5Ah triangle battery. 52V is worth the upgrade here — the BBSHD benefits from the voltage headroom on sustained climbs.
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Cargo bike build or very heavy rider
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.
Get Your Bafang Fitted in Cardiff
Full fitting service
Motor, battery, display, cable routing, and programming — all completed in our Roath workshop.
Supply only
Prefer to DIY? We supply BBS kits with UK next-day delivery. Ask us on WhatsApp to confirm compatibility.
Repairs & upgrades
Already have a Bafang and need it reprogrammed or upgraded? See our service menu.
Visit us: 2 Beresford Road Lane, Cardiff, CF24 1QU
Hours: Mon–Fri 11am–6pm • Sat 11am–3pm • Sun closed
FAQ
Is a Bafang BBS02B legal in the UK?
Yes — when programmed correctly. The BBS02B must be configured to deliver no more than 250W continuous assist, assist only when pedalling, and cut off above 15.5 mph (25 km/h) to comply with UK EAPC regulations.
What bottom bracket size do I need for a Bafang mid drive?
The BBS01B and BBS02B require a 68mm or 73mm threaded English (BSA) bottom bracket shell. The BBSHD requires a 100mm BSA shell. Press-fit and PF30 shells need specialist adaptors.
How much does a Bafang conversion cost in the UK?
A BBS02B kit with battery typically costs £350–£500. A complete installed BBS02B build with a 48V 15Ah battery is usually in the range of £600–£800 all-in.
Can I fit a Bafang mid drive to a carbon frame?
Yes, but it requires more care than steel or aluminium. Carbon BB shells can crack if the motor lock ring is over-torqued. We handle carbon builds at our Cardiff workshop — we do not recommend DIY installation on carbon frames.
Will a Bafang mid drive wear out my chain and cassette faster?
Yes — this is an honest trade-off with any mid drive system. Because the motor drives through the chain, component wear is higher than with a hub motor. Using a quality chain and a steel chainring, and changing your chain regularly at 0.5% stretch, significantly extends drivetrain life.
Seeing a fault on the display after fitting? Our guide to Bafang error codes explains what each one means.
Still have questions about your specific frame or build? Message us on WhatsApp with your frame details and how you intend to use it — we’ll give you a straight answer and a recommendation.
