E-Bike Conversion Kit UK: The Complete Buyer’s Guide
Converting an existing bike to electric is one of the most cost-effective ways to get into e-cycling — or to breathe new life into a frame you already love. The UK market for conversion kits has matured considerably, and the choice between mid-drive and hub motor systems is no longer a coin flip. This guide walks you through every major option so you can buy with confidence.
Mid-Drive vs Hub Motor: The Fundamental Choice
Before looking at specific kits, you need to settle on the drive architecture. This single decision shapes everything that follows.
Mid-Drive Motors
Mid-drive units bolt to the bottom bracket and drive the chain directly. Because the motor works through the bike’s own gears, it stays in its efficient torque band on hills and carries less rotating mass at the wheel. Handling remains closer to a standard bike. The trade-off: higher cost, more complex fitting, and the drivetrain — chain, cassette, chainring — wears faster under the added load.
Hub Motors
Hub motors sit inside a replacement front or rear wheel. Installation is simpler, costs are lower, and there are fewer mechanical interactions with the rest of the drivetrain. The drawback is that a hub motor operates at a fixed gear ratio to the wheel, which means it can struggle on sustained climbs and runs less efficiently than a mid-drive on hilly terrain. For flat urban commuting, the difference is minimal.
If your riding is predominantly flat or you are on a tight budget, a hub kit is a perfectly rational choice. For hilly routes, loaded touring, or off-road use on private land, mid-drive pulls ahead.
Mid-Drive Kits: Which Bafang — or TSDZ2?
Bafang dominates the mid-drive conversion market in the UK, with four distinct motors covering a wide performance and budget range. The TSDZ2 from Tongsheng offers a different philosophy worth considering.
Bafang BBS01B — Budget and City Riding
Power rating: 250W (EAPC-compliant as standard).
The BBS01B is the entry point to Bafang’s BBS range and the natural choice if you want a road-legal setup that complies with UK EAPC rules — 250W continuous output, pedal-assist only to 15.5 mph. It suits lightweight city bikes and hybrids used for commuting or leisure on flat to gently rolling terrain. Motor weight is manageable, and the lower price means the total conversion cost is achievable for most budgets. Do not expect it to haul heavy loads or climb steep hills with any urgency.
Bafang BBS02B — The Most Popular Kit
Power rating: 750W (for off-road / private land use at full power; can be limited for EAPC compliance).
The BBS02B is the kit most conversion specialists reach for first. It strikes the right balance between power, weight, and price for the majority of riders. It handles hills competently, works well on mountain hardtails and trekking bikes, and the torque output is enough to make a real difference on loaded commutes or mixed terrain. The programming interface (via USB and Bafang configuration software) gives experienced users meaningful control over power curves and assist levels. This is our most recommended starting point for anyone who rides varied terrain.
Bafang BBSHD — Heavy-Duty Mountain
Power rating: 1,000W.
The BBSHD is built for demanding use: mountain bikes, fat bikes, cargo frames, and riders who need sustained high power output. The motor is substantially heavier and larger than the BBS02B — bottom bracket clearance and frame compatibility need careful checking. It generates significant heat under sustained load, so it rewards riders who understand motor management. For private land trail riding on capable frames, it is a compelling option. Not appropriate for road-legal builds at full power.
Bafang M620 — Ultra-Powerful Mid-Drive
Power rating: up to 1,000W+ with high torque output.
The M620 (also known as the Ultra) represents the top of Bafang’s consumer mid-drive range. It uses a different internal architecture — a planetary gear system rather than the nylon gear found in the BBS series — and is rated for sustained high loads. Torque figures are exceptional. Frame requirements are more demanding: specific bottom bracket shell dimensions and motor-mount compatibility must be confirmed before purchase. If you are building a serious off-road machine on private land, the M620 is worth the premium. Overkill for anything road-legal.
TSDZ2 — Torque-Sensing Mid-Drive
Power rating: 250W–500W depending on variant.
The TSDZ2 takes a different approach to pedal assist. Where Bafang kits use cadence sensing (the motor kicks in when you pedal, regardless of how hard), the TSDZ2 uses torque sensing — the harder you push, the more assistance you receive. The riding feel is noticeably more natural, closer to a quality branded e-bike than most conversion kits. It is a popular choice for riders who dislike the on/off character of cadence-based systems and want a more intuitive, ride-feel-focused conversion. The 250W variant is EAPC-compliant. The firmware community around the TSDZ2 (open-source firmware is available) means technically confident riders can tune it extensively.
What to Consider Before You Buy
Bike Compatibility
Mid-drive kits require a specific bottom bracket shell diameter — most BBS kits fit 68mm or 73mm threaded shells, but press-fit, PF30, and other modern standards need an adapter or are simply not compatible. Check your frame’s specification sheet before ordering. BBSHD and M620 also need adequate clearance around the bottom bracket for the motor housing.
Hub kits need wheel size compatibility (26-inch, 27.5-inch, 29-inch, 700c) and dropout width confirmation. Most modern rear hubs are 135mm quick-release or 142mm thru-axle — confirm before buying.
Budget
As a rough guide for complete kits including battery:
- Hub motor kit: from around £300–£500
- BBS01B complete: from around £400–£600
- BBS02B complete: from around £500–£800
- BBSHD / M620 complete: from around £800–£1,200+
- TSDZ2 complete: from around £500–£750
Battery voltage and capacity significantly affect cost. A 48V 17.5Ah pack costs meaningfully more than a 48V 10Ah pack, but the range difference is real.
Intended Use
Be honest about how you ride. A flat 10-mile urban commute on a hybrid calls for a completely different kit to a technical off-road trail session on private land. Overpowering a lightweight city bike is wasteful and can stress the frame. Underpowering a mountain bike on steep climbs is frustrating. Match the motor to the riding, not to the spec sheet.
Road-Legal Builds: What the Law Requires
For a converted e-bike to be ridden on UK public roads without registration, insurance, or a licence, it must meet EAPC rules: motor rated at 250W maximum continuous output, pedal-assist only (no throttle-only propulsion), and assistance cutting off at 15.5 mph. A BBS01B or TSDZ2 250W variant can be configured to comply. Higher-powered kits can be limited in software, but the motor’s rated power determines its legal classification — if in doubt, check with the DVLA.
Ready to Choose?
Browse VOLTARC’s range of conversion kits — mid-drive and hub kits including full battery-included bundles. If you are unsure which kit suits your frame, get in touch — we will give you a straight answer based on your actual setup, not an upsell.