Confused by e-bike jargon? This glossary defines every term you'll encounter when researching, buying, and installing an e-bike conversion kit.
The e-bike world has its own vocabulary, and if you're new to conversion, you'll encounter dozens of unfamiliar terms — BMS, cadence sensor, Hall effect, PAS, torque arm, and many more. This glossary defines every term you need to know, organized alphabetically with plain-English explanations and links to deeper guides where applicable.
Bookmark this page — you'll reference it constantly during your first conversion.
A-B
Amp (A): The unit of electrical current. Higher amps = more power delivery. Most e-bike motors draw 10-30A at peak.
Amp-hour (Ah): The capacity of a battery. A 15Ah battery can deliver 15 amps for one hour, or 1 amp for 15 hours. Multiply by voltage to get watt-hours (Wh).
BafangConfigTool (BCT): Free software for programming BAFANG BBS02/BBSHD motors. Lets you customize assist levels, throttle response, speed limits, and dozens of other parameters.
BBS02: BAFANG's 750W mid-drive motor, in production since 2014. The most-installed DIY e-bike motor in history.
BBSHD: BAFANG's 1000W mid-drive motor, the bigger brother to the BBS02. Heavier and more powerful.
BMS (Battery Management System): The circuit board that protects a lithium-ion battery from overcharge, over-discharge, over-current, and short circuits. The most important safety component in your battery.
Bottom bracket (BB): The cylindrical shell on a bike frame where the crankset attaches. Mid-drive motors replace the standard bottom bracket.
Brushless motor: The type of motor used in all modern e-bikes. No physical brushes to wear out, more efficient than brushed motors.
C-D
Cadence sensor: A simple magnetic sensor that detects whether you're pedaling. The motor delivers preset power based on assist level, regardless of how hard you're pedaling. Compare to torque sensor.
Cassette: The cluster of gears on the rear wheel. Mid-drive motors drive through the cassette via the chain.
Charge cycle: One full discharge and recharge of a battery. E-bike batteries typically last 500-1000 charge cycles before significant capacity loss.
Class 1 e-bike: Pedal-assist only, no throttle, max 20mph. The most trail-friendly e-bike class.
Class 2 e-bike: Throttle-equipped, max 20mph. Treated like a regular bicycle in most states.
Class 3 e-bike: Pedal-assist only, max 28mph. Often restricted from certain bike paths.
Controller: The 'brain' of an e-bike. Manages power flow between battery, motor, and your inputs. Sits between all the components.
CYC Photon: A lightweight high-power mid-drive motor from CYC Motor. Alternative to BAFANG BBSHD for weight-conscious builders.
E-H
E-bike: Short for electric bicycle. A bicycle with an electric motor that assists with propulsion.
Endless Sphere: The largest e-bike DIY forum. The go-to resource for technical questions and community knowledge.
Fat bike: A bike with very wide tires (4-5 inches) designed for snow, sand, and soft terrain. Excellent conversion candidates for off-road use.
Freewheel: A mechanism that allows the rear wheel to keep spinning when you stop pedaling. Standard on all modern bikes.
Gearless hub motor: A type of hub motor with no internal gears. Simpler and more durable than geared hub motors, but heavier and less torquey. Also called 'direct drive'.
Geared hub motor: A hub motor with internal gears that multiply torque. Lighter and more torquey than gearless, but the gears can wear out.
Hailong: A battery form factor that slides onto a down-tube mounted dock. The most common budget e-bike battery style.
Hall sensor: A magnetic sensor inside brushless motors that tells the controller the rotor's position. Required for proper motor commutation.
Hub motor: A motor located inside the wheel hub (front or rear). Compare to mid-drive.
I-M
IP rating: Ingress Protection rating. Indicates how well a component resists dust and water. IP65 is the minimum for e-bike motors used in rain.
Lithium-ion (Li-ion): The battery chemistry used in all modern e-bikes. High energy density, low self-discharge, but requires careful management to prevent fires.
Low-voltage cutoff (LVC): A controller setting that shuts off the motor when the battery voltage drops too low. Prevents battery damage from over-discharge.
Mid-drive: A motor mounted at the bottom bracket that drives through the bike's chain and gears. Compare to hub motor.
MOSFET: The type of transistor used in e-bike controllers to switch power to the motor. Quality controllers use name-brand MOSFETs (Infineon, IR); cheap controllers use generic MOSFETs that fail faster.
Motor stator: The stationary part of a brushless motor. The spinning part is the rotor.
N-R
Nominal wattage: The motor's continuous power rating. The US federal e-bike limit is 750W nominal. Compare to peak wattage.
Open-source firmware (OSF): Custom firmware that replaces the manufacturer's stock firmware. Available for BAFANG BBS02/BBSHD (BafangConfigTool) and Tongsheng TSDZ2 (TSDZ2 OSF project).
PAS (Pedal Assist Sensor): The system that detects when you're pedaling and tells the motor to provide assist. Can be cadence-based or torque-based.
Peak wattage: The motor's maximum momentary power output. Typically 1.5-2x nominal wattage. A 750W motor might produce 1,400W peak during hard acceleration.
Phase wire: The three thick wires connecting the controller to the motor. Carry the high-current three-phase AC power that drives the motor.
Press-fit bottom bracket: A bottom bracket that's pressed into the frame rather than threaded. Cannot accept mid-drive motors without adapters — avoid for conversion.
S-T
Shark battery: A battery form factor similar to Hailong but with a more refined case. Common on premium e-bikes.
Sine wave controller: A controller that delivers power in a smooth sinusoidal pattern. Smoother and quieter than square wave controllers. Preferred for quality builds.
Square wave controller: A simpler, cheaper controller that switches power abruptly. Noticeable torque ripple and more noise than sine wave.
Step-through frame: A bike frame with a low top tube, allowing the rider to step through rather than swing a leg over. Excellent conversion candidate for utility riders.
Tektro: A popular brake brand. Their hydraulic disc brakes are commonly used on e-bike conversions.
Throttle: A twist grip or thumb lever that delivers motor power on demand, without pedaling. Standard on most US e-bike kits.
Torque arm: A metal bracket that prevents a hub motor's axle from spinning inside the fork dropouts. Mandatory for all hub motor installs.
Torque sensor: A sensor that measures how hard you're pedaling, in real time. Power delivery is proportional and smooth. Compare to cadence sensor.
TSDZ2: Tongsheng's mid-drive motor with a true torque sensor. The original torque-sensor DIY option since 2017.
TSDZ8: Tongsheng's upgraded mid-drive (released 2024). More power and better cooling than TSDZ2.
U-Z
UL 2271: A safety certification for lithium-ion batteries. The gold standard for battery safety; rare on budget Amazon batteries.
UPP (Unit Pack Power): A budget battery brand. We do NOT recommend UPP due to ongoing safety litigation and documented fire incidents.
Varstrom: A budget e-bike kit brand that rebrands BAFANG and Tongsheng motors. Generally good quality and warranty support.
Voilamart: A budget e-bike kit brand. The cheapest reputable 1000W hub kit on Amazon.
Voltage (V): The 'pressure' of electricity. Higher voltage = more top speed and torque. Most modern e-bikes are 48V; performance builds use 52V.
Watt (W): The unit of electrical power. Calculated as volts × amps. A 48V motor drawing 20A produces 960W.
Watt-hour (Wh): The actual energy capacity of a battery. Calculated as volts × amp-hours. The number that matters for range calculations.
Wh per mile: The energy consumption rate of an e-bike. Typical values: 15-25 Wh/mi for moderate assist, 30-50 Wh/mi for throttle-only.
XT60 connector: A popular battery connector rated for 60A. Common on quality e-bike batteries and controllers.