The motor system is the most important specification when choosing an e-bike. Not the battery capacity, not the display, not the frame — the motor determines how the bike feels to ride. This guide explains the key motor types, how to compare them, and which systems are right for different riders.
Hub Motor vs Mid-Drive: The Fundamental Choice
Hub Motors (Rear or Front Wheel)
Hub motors are integrated into the wheel hub. They push or pull the bike regardless of what gear you are in — the motor’s power is independent of the drivetrain. This is their key limitation: on steep hills, the motor is working inefficiently because it cannot use the mechanical advantage of lower gears. Hub motors are simpler, cheaper, and require less maintenance than mid-drives. A rear hub motor is nearly invisible on a bike. For flat terrain and moderate gradients, they are perfectly adequate and cost-effective.
Mid-Drive Motors
Mid-drive motors sit at the bottom bracket and drive through the bike’s gears. In a low gear, the motor produces much more effective climbing force than in a high gear — exactly like your legs. This makes mid-drives significantly more efficient on hills and gives them better overall range on hilly terrain. The drivetrain also takes more stress — chains and cassettes wear faster on a high-power mid-drive. Mid-drives are heavier than hub motors but typically provide better handling because the weight is centralised.
Motor Systems by Brand
| System | Type | Max torque | Best for | Typical UK bike brands |
|---|---|---|---|---|
| Bosch Performance Line CX | Mid-drive | 85 Nm | MTB, hilly commuting, cargo | Cube, Trek, Cannondale, many |
| Shimano EP8 | Mid-drive | 85 Nm | MTB, road, commuting | Giant, Orbea, Scott |
| Shimano STEPS E5000/E6100 | Mid-drive | 40-60 Nm | Commuting, leisure | Various mid-range brands |
| Fazua Ride 60 | Mid-drive | 60 Nm | Road, light MTB | Canyon, Pinarello, Felt |
| Brose Drive S Mag | Mid-drive | 90 Nm | MTB (Specialized Levo) | Specialized |
| Mahle X35+ | Rear hub | 40 Nm | Road, commuting | Various, some Ribble |
| Bafang BBS02B | Mid-drive (conversion) | ~100 Nm | Conversions, off-road | Kit (fit to existing frame) |
| Generic hub motors | Rear hub | 30-50 Nm | Budget commuting | Budget brands, Halfords |
Torque: What the Numbers Mean
Motor torque (Nm) tells you how much twisting force the motor applies. Higher torque means more effective hill-climbing and stronger acceleration. For context: an average fit cyclist produces 50-100 Nm at the pedals during normal riding, and up to 200 Nm in a sprint. An 85 Nm motor (Bosch CX, Shimano EP8) effectively doubles your pedal force on climbs — the difference between 40% effort and 80% effort going up a steep gradient. For flat commuting, a 40 Nm motor is ample. For hill climbing, 60 Nm+ makes a meaningful difference.
Power Output and UK Law
For EAPC compliance (road legal in the UK), the motor must be rated at 250W maximum continuous power and cut assistance at 15.5 mph. All the OEM systems listed above (Bosch, Shimano, Fazua, Mahle, Brose) are rated at 250W continuous and are EAPC-compliant when fitted to an appropriately-configured bike. The Bafang BBS02B is 750W rated — it requires programming to limit it to 250W for road-legal use.
Cadence Sensor vs Torque Sensor
Budget e-bikes often use cadence sensors — they detect pedal rotation and apply motor power when you pedal. All OEM mid-drive systems (Bosch, Shimano, Fazua, Brose) and the TSDZ2 use torque sensors — they measure how hard you push and apply proportional assistance. Torque sensing feels more natural and is significantly more efficient. If you are choosing between two bikes at similar price points, a torque-sensing system is worth prioritising over a cadence-sensing one.