Best Rear Hub Motor eBike Conversion Kit: 250W to 8000W Compared
Short answer
For a road-legal UK commuter, a 250W rear hub motor set up as pedal-assist only, with a 25 km/h cutoff, is the simplest and most affordable choice. Hub motors above 250W are sold for off-road and private land use only, so for those builds 1500W to 3000W covers most riders. Match the battery voltage to the motor, and pick capacity for your wattage and how far you ride.
About this guide: We have built and fitted rear hub motor conversions at the All4eBikes Cardiff workshop across the full range — from 250W commuter builds to 8000W off-road machines. The comparisons below are based on what we have actually seen these motors do on real bikes, not manufacturer marketing figures.
What a Rear Hub Motor Actually Does
A rear hub motor conversion replaces your existing rear wheel with a purpose-built wheel that has the motor laced directly into the hub. The motor drives the wheel independently of your gears — unlike a mid drive, it doesn’t care what gear you’re in, because it never touches the chain or cassette. Fitting one means swapping the wheel, mounting a controller and battery, and connecting a throttle and/or pedal assist sensor and display.
This simplicity is the whole appeal. There is no bottom bracket to remove, no chainline to worry about, and drivetrain wear is effectively unaffected since the motor’s power never passes through the chain.
Geared vs Direct-Drive Hub Motors
Almost every hub motor we sell is a geared brushless motor rather than a direct-drive unit, and the difference matters when comparing kits.
Geared hub motors
- Smaller and lighter for a given torque output
- Freewheel when the motor isn’t powered — no drag when pedalling unassisted
- Better low-speed torque, which means stronger hill starts
- Internal gearbox is a wear item, though a well-built unit lasts many thousands of miles
Direct-drive hub motors
- No internal gearbox — fewer moving parts to wear out
- Heavier and larger for the same power output
- Some drag when unpowered unless the controller supports freewheeling
- Capable of regenerative braking, which geared motors typically are not
- Usually only found in our higher-wattage, off-road focused kits
For the vast majority of riders — commuters and hill riders in particular — a geared motor is the better everyday choice, which is why it’s what we stock across the 250W to 3000W range.
Wattage Tiers Compared
| Wattage | Real-world performance | Road legal in UK? | Typical use case |
|---|---|---|---|
| 250W | Strong assist on flat and moderate terrain. Comfortably eliminates headwind fatigue. Works harder on sustained steep gradients, especially with a heavier rider. | ✓ Yes (PAS only, 25 km/h cutoff) | Urban and suburban commuting |
| 500W–1000W | Noticeably stronger hill-climbing and faster acceleration from a standstill. Handles loaded panniers or a heavier rider without strain. | ✗ Off-road/private land only | Hillier commutes off the public highway, cargo use |
| 1500W–3000W | Serious torque and top speed. Comfortably handles steep off-road climbs and heavy loads. This is where most of our off-road and trail-focused customers land. | ✗ Off-road/private land only | Trail riding, private land, heavy cargo builds |
| 3000W–8000W | High-speed, high-torque performance builds. Requires a frame, wheel, and braking setup rated for the extra stress and speed involved. | ✗ Off-road/private land only | Speed builds, dedicated off-road machines |
A common mistake: Buying more wattage than the riding actually calls for. A 3000W hub motor on a bike that’s mostly used for a flat 5-mile commute adds weight, cost, and battery drain for performance that’s rarely used. Match the wattage to the terrain and the use case, not to the biggest number available. If hills are the deciding factor, our guide to hub motors on steep hills covers what to look for.
UK Road Legality for Hub Motor Kits
Only a 250W hub motor, configured as pedal-assist-only with a 15.5 mph (25 km/h) cutoff, meets the UK’s EAPC (Electrically Assisted Pedal Cycle) rules and can be ridden on public roads without a licence, insurance, or registration. Every hub motor kit above 250W that we sell is sold and intended for off-road and private land use only — there is no way to detune a 1500W+ hub motor back down to a legally compliant EAPC specification in the way a Bafang mid drive can be reprogrammed.
For the full legal picture, including what counts as pedal assist, throttle rules, and the consequences of riding an unregistered high-powered conversion on the road, see our complete UK eBike legality guide.
Matching a Battery to Your Hub Motor
Voltage must match your motor and controller, and capacity should match both your wattage tier and how far you actually want to ride. You can browse the full eBike battery range to compare voltage and capacity options directly.
| Motor wattage | Voltage | Minimum capacity | Recommended capacity |
|---|---|---|---|
| 250W | 36V | 10Ah (360Wh) | 13–15Ah (468–540Wh) |
| 500W–1000W | 48V | 13Ah (624Wh) | 17.5Ah (840Wh) |
| 1500W–3000W | 48V or 72V | 17.5Ah (840Wh) | 20Ah (960Wh+) |
| 3000W–8000W | 72V | 20Ah (1440Wh) | 25Ah+ with a high continuous discharge rating |
Above 1500W, discharge rate (C rating) matters as much as capacity — a battery that can’t supply the current a high-power motor draws under load will sag in voltage and shorten its own lifespan. Look for a continuous discharge rating of at least 30A for anything in the 1500W+ range.
Frame and Wheel Compatibility
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Check your rear dropout width
Most standard bikes use a 135mm or 142mm rear dropout. Confirm which your frame has before ordering — most of our hub motor kits are built for 135mm dropouts, and 142mm thru-axle frames need a different wheel build or adapter.
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Confirm your wheel size
Hub motor wheels are pre-built to specific diameters. Check whether your bike runs 26”, 27.5”, or 700c/29” wheels, and make sure the kit you order matches. Fat tyre bikes need a specific wider-hub variant.
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Check your braking system
Higher wattage kits reach higher top speeds, and your brakes need to be able to safely stop that speed. We recommend hydraulic disc brakes for anything above 750W, and strongly recommend them above 1500W.
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Rule out rear suspension complications
Full-suspension frames make hub motor installation more complex — the motor cable has to cross the pivot point without snagging or stretching through the suspension travel. It’s still doable, but worth flagging to us before you order if this applies to your bike.
Which Hub Motor Kit Should You Buy?
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Flat commute, want it road-legal
250W 36V hub motor + 36V 13Ah downtube battery. The simplest, most affordable, fully road-legal option. Ideal for routes under 15 miles each way with limited climbing.
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Hilly commute, road use isn’t required
500W–1000W hub motor + 48V 17.5Ah battery. A meaningful step up in climbing ability for private land or off-highway routes.
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Off-road trail riding, private land
1500W–3000W hub motor + 48V or 72V battery with a triangle mount. Handles steep, technical terrain confidently. Consider a Bafang mid drive instead if your frame has a compatible bottom bracket — the gear advantage often outperforms an equivalent-wattage hub motor on steep, technical trails.
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Heavy cargo or high rider weight
1500W–2000W hub motor for straightforward rear-drive torque. Simpler and more tolerant of sustained heavy loading than a mid drive, since there’s no drivetrain stress to manage.
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Not sure — want advice on your specific bike
Message us on WhatsApp before you order. Tell us your frame, dropout width, wheel size, and intended use, and we’ll recommend the right wattage and battery combination.
Visit us: 2 Beresford Road Lane, Cardiff, CF24 1QU
Hours: Mon–Fri 11am–6pm • Sat 11am–3pm • Sun closed
FAQ
Is a rear hub motor better than a front hub motor?
For most conversions, yes. A rear hub motor puts power through the wheel that carries more of the rider’s weight, which gives better traction, especially when climbing or accelerating. Front hub motors are lighter to fit and keep the rear wheel free for gearing, but can struggle for grip under hard acceleration or on loose surfaces, and handling can feel less natural under power. We fit rear hub motors as the default recommendation for the vast majority of builds.
What is the most powerful road-legal hub motor kit?
250W is the maximum continuous output permitted for a UK road-legal EAPC conversion, regardless of the motor’s peak rating. There is no way to make a 500W+ hub motor kit road-legal in the way a programmable Bafang mid drive can be detuned. If you need higher power on public roads, the only legal options are registering the vehicle as a moped or motorcycle, which involves different licensing, insurance, and construction requirements entirely.
How long does a hub motor last?
A well-built geared hub motor, used within its rated power and not consistently overloaded, typically lasts several thousand miles before the internal gearbox needs attention. Direct-drive motors, having no internal gearbox, generally last longer but are heavier and less common in our range. Water ingress, consistent overheating from riding above the motor’s rated power, and impact damage are the most common causes of premature failure.
Can I fit a hub motor to a bike with disc brakes?
Yes — most of our hub motor wheels are available in both disc brake and rim brake versions. Confirm which braking system your bike uses before ordering, since the wheel build differs. For anything above 750W, we recommend disc brakes for the additional stopping power the higher speeds and torque demand.
Do I need a throttle, pedal assist, or both?
For a road-legal 250W build, the motor must be pedal-assist-only under UK law — a throttle that can propel the bike without pedalling makes the conversion illegal for road use. For off-road builds above 250W, a throttle is common and useful for technical terrain where pedalling smoothly isn’t always possible, and most riders run both a pedal assist sensor and a throttle together.
Not sure which hub motor wattage and battery combination suits your bike? Message George on WhatsApp with your frame details and typical ride — we’ll give you a direct recommendation.
