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Understanding Electric Bike Terminology

Posted by Trevor James on

Take a look at this image. It pretty much breaks down all the different parts of an electric bike. Keep in mind that an e-bike is exactly the same as a regular bicycle, but with special electrical components worked into the bicycle in different parts. Also, keep in mind that all e-bikes are different. There are many different ways to position the battery, the motor, the controller, the computer, and the throttle. But this image will give you a great idea of the basics of e-bike terminology.

e-bike terminologyLet’s discuss these terms one by one:


Rear fender/Mud Flap – Fender is the American English term for the part of an automobile, motorcycle or other vehicle body which frames a wheel (the fender underside). Its main function is to prevent sand, rocks, mud, road spray and liquids from being hurled into the air by the rotating tire. Fenders are usually rigid and could be damaged by contact with the road surface.

Saddle rack – A saddle rack is a framework, bracket, or stand where a saddle may be hung when not in use.

Seat stay – On a bicycle, a seat stay is one of the parallel tubes that run from the top of the seat tube back to the rear axle.

Rear hub motor – A rear hub motor also called a wheel hub motor is an electric motor which is incorporated into the hub of a wheel and drives it directly.

Rear dropouts – Rear dropouts are the two small notches in the rear of your bicycle where the hub rests.  It is where your rear wheel goes.

Spokes – Spokes are rods radiating from the center of a wheel, connecting the hub with the round traction surface.

Freewheel cassette – A freewheel cassette is a profiled wheel with teeth or cogs, that mesh with a chain, track or other perforated or indented material.

Rail Derailleur – A rail derailleur is a gear-shifting mechanism on a bicycle which shifts the drive chain from one sprocket wheel to another.

Chain stay – A chainstay is one of the two tube frames which run horizontally from the bottom bracket shell back to the rear dropouts.

Chain – The bicycle chain is a chain that transmits power from the pedals to the driving wheel of a bicycle.

Pedelec Sensor – A pedelec sensor is a mechanism that sends signals to the controller to indicate that the pedals are moving.

Crank arm – is the offset portion of a crankshaft to which the connecting rod and piston are attached.

Pedal – a leverlike part worked by the foot to supply power in several mechanisms as in an electric bicycle.

Down tube – a vertical tube that makes up part of the bicycle frame.

Cable housing  –  a sheath that provides covering for the electric bicycle’s cables.

Front Hub and Axle – The hub is the center part of a bicycle wheel. It comprises of an axle, bearings and a hub shell. The hub shell usually has two machined metal flanges to which spokes can be attached. The axle is attached to dropouts on the fork or the frame. It is a rod that attaches a wheel to a bicycle and provides support for bearings on which the wheel rotates.

Rim – The rim is the outer edge of a wheel holding the tire. It makes up the outer circular design of the wheel on which the inside edge of the tire is mounted on vehicles such as automobiles.

Disc brake caliper – In a disc-braking system the bike’s wheels are attached to metal discs, or rotors, that spin along the wheels. The job of the caliper is to slow the bike’s wheels by creating friction with the rotors.  The bike caliper fits over the rotor like a clamp.

Disc brake – A disc brake is a kind of brake which uses calipers to squeeze pairs of pads against a rotor in order to create friction that retards the rotation of a shaft, such as a vehicle axle, either to reduce its rotational speed or to hold it stationary.

Fork – A bicycle fork is the part of the bicycle that holds the front wheel. A fork usually consists of two blades which are joined at the top by a fork crown. Above the crown, a steerer tube attaches the fork to the bicycle and the handlebars (through a stem) allowing the user to steer the bicycle.

Valve stem – A valve stem is a self-contained valve which opens to admit gas to a chamber such as air to inflate a tire and is then automatically closed and kept sealed by the pressure in the chamber, or a spring, or both, to prevent the gas from escaping.

Brake lever -  is a lever on the handlebar that connects to the brake cable and thus operates the braking mechanism.

Handlebar – refers to the steering mechanism for bicycles; the equivalent of a steering wheel.

Twist throttle – is the device, lever or pedal that controls the quantity of energy, electricity or fluid going to the motor and is used to control the electric bicycle’s speed.

Twist Grip Shifter – is a component used to control the gearing mechanisms and select the gear ratio.

Head tube – is the part of the electric bicycle’s tubular frame within which the front fork steerer tube is mounted.

Top tube – the top tube or cross-bar connects the top of the head tube to the top of the seat tube.

Seat post – is a tube that extends upwards from the bicycle frame to the saddle.

Controller  - there are two kinds of controllers designed to match either a brushed motoror brushless motor. The controller is the brain of electric bikes. It is connected to all other electronic parts like the battery, motor and throttle. It takes all inputs from other components and determine what should be signaled to them in return.

As an electric bike user or someone who is interested in electric bicycles, you might also want to really familiarize yourself with the important parts, of the e-bike, electric bike jargons along with some accessories.

Hub Motor. This kind of motor exists within an enlarged hub and is built-in directly to the front or rear wheel with special spokes. It drives the bicycle through the application of torque directly to the wheel and is generally more silent and more efficient compared to external chain driven motors. Hub motors could be geared or ungeared and come in many Watt sizes.

Motor Watts. This is the unit of power defined as one joule per second used to measure the size of an electric bike motor. Higher Watt motors mean faster and stronger e-bikes but it also depends on the battery volts.

Battery Volts. It refers to the electric power potential that the battery supplies to the motor giving the bicycle torque as well as hill climbing ability. Just imagine a garden hose and a fireman’s hose. More water could come out at once from the fireman’s hose so that is equivalent to higher voltage and will increase motor performance.

Battery Amp Hours. This is the unit of electric charge a battery can handle and determines how long the battery would last. Higher amp-hours will make the battery go further.

Brushed vs. Brushless. This is a description of how the motor is built, brushless means more silent motors because there are no “brushes” rubbing to make the motor go. Brushless also lasts longer.

Geared Motor. Gears are used to convert higher rotations per minute (RPM) in the motor into more or less torque. A lot of bike gears but some cheaper bicycles use plastics that could wear out faster over time or become noisier. Some bikes and trailers use chains and rings instead, like gears on your bicycle. If gears are external versus the inside of a hub motor they could wear out faster because they are exposed to the elements.

PAS  or Pedal Assist. Electric bikes with pedal assist options sense the revolutions of your front crank. There is a small plate with sensors and magnets in it mounted right where the pedals go through the bike frame and every time the pedals goes by it signals the bike motor to help you. Oftentimes the bikes have changing levels of aid to either make your ride easier but use up the battery faster or harder and have the battery last longer.

Twist and Go (TAG). Throttle mode or twist and go mode is just the default electric drive mode that only  powers the bike as you twist a throttle or push a lever. In this mode, pedal assist is disabled.

Sealed Lead Acid or SLA. This kind of battery is cheaper and easier to recycle. Hence, it is better for the environment and geopolitics because Lithium is often mined in politically unstable parts of the world. The disadvantage is that they are a lot heavier and will only last 1/3 as long as other alternatives such as Lithium ion. They usually last somewhere between 300 and 500 cycles.

Lithium polymer (Li-Poly). This kind of battery is a step up from Sealed Lead Acid and is going to make make your bicycle go further but also cost more. It does not have quite as much surface area as Lithium Ion because the lithium-salt electrolytes which store energy are suspended in a polymer composite like polyethylene oxide or polyacrylonite. The benefit is that this kind of battery is very rugged.

Lithium Iron Phosphate (LiFePO4). This kind of battery is another mid-level option which is stable and has a longer lifespan compared to Sealed Lead Acid. It is similar in performance compared to Lithium Polymer but could be heavier.

Lithium Ion. This kind of battery is the most desirable because it gives the most charge cycles, close to 1500 and is also very light. It is also the most expensive and has been unstable in a few applications in the past. Newer Li-ion batteries are everywhere from laptops to cellphones and electric bicycles.

AC Current. Alternating current is used in electrical mains but very rarely used in light electric vehicles.

Advanced battery. A battery using NiMH or Lithium cells, usually needing a battery management system (BMS) with higher performance and higher cost.

After Market Kit. A kit of components to convert a manual bicycle to an electric bicycle.

Amp. From Ampere, it is a measure of the amount of electrical current that passes through any given point given a certain amount of time. It is used to describe the demand or supply of electrical energy.

Auxiliary battery. It is a battery which could provide current to the vehicle, but is optional, or extra, or added on.

Battery, or Energy Storage Device. It is a combination of cells that make a certain voltage and current capability to power an electric motor or vehicle.

Battery Box, or Battery Package. It is the combination of cells which make up a battery which provides electrical energy for the electric bicycle. It is packed into the unique form factor for a certain vehicle. It usually goes with BMS or motor controller inside the same box.

Bottom Bracket Motor. It is a motor located in or adjacent to the bottom bracket or pedal axle. It is sometimes called a central motor or mid motor.

BMS. It stands for Battery Management System and is an electronic circuit which is found on advanced batteries. The BMS protects the battery from damage, and prevents safety problems of battery overheating and also monitors the state of charge.

Brake Kill Switch. It is a device which turns off the motor as the brake lever is applied by the user.

C-Rate. It is a unit of measurement which describes how fast a battery could supply current. A 1c rate means that the battery could be completely discharged in a single hour. Going faster than that will simply not work or could damage the battery. A 2c rate battery could be discharged in 30 minutes, or twice as fast as a 1c rate battery. This is important with regards to the power which could be developed by the motor attached to the battery. For example, a 500 watt motor which is climbing a hill could demand 30 amps of energy. If the battery is a 10 ah battery, then it has to supply energy at a 3c rate to let the motor do its job. If the battery is only capable of 1c, the rider would likely walk on this hill.

Cells. Individual electro chemical devices which create electric current and are combined in packages to give the right amount of voltage and current for a certain function, called batteries.

Ceramic Magnets. They are used in electric motors. It is lower in performance and cost compared to Neodymium magnets.

Connectors. These are the fittings which allow the electrical components and wiring that need to be connected. They are often easily released or unplugged.

Coulombs. Units of measurement of energy. The amount of energy is equal to one amp for one second. Therefore, there are 3600 coulombs in a single amp hour. Since the battery state of charge for lithium is hard to ascertain by the measurement of voltage, sophisticated BMS measure the SOC of lithium batteries by counting coulomb.

Current. A flow of electricity that normally refers to the amount of electrical energy being used by the electric bicycle.

DC. This stands for direct current or the form of electric current used in almost all light electric vehicles.

DC Motor.  This refers to a motor that uses direct current.

Direct drive motor. This is a reference to a hub motor which has no gear reduction. These motors are quieter and simpler. They are often more expensive and larger compared to gear type motors.

DIY kit. This stands for do-it-yourself kit which is a set of components that convert a manual bicycle to an electric bicycle.

EPAC. It stands for Electric Pedal Assist Cycle or European Union law calls an electric bicycle.

Gear Type Motor. This usually refers to a hub motor which uses a gear reduction inside the hub shell. These motors are usually cheaper and have good performance but are noisy and have more wear points.

Human Electric Hybrid. This is an electric bicycle which allows both human and electric power. It is a very efficient system as humans are low endurance, high torque devices and electric motors are lower torque, high endurance devices that are limited only by the battery. Together they are a very efficient and effective propulsion system for a vehicle.

ICE. This stands for internal combustion engine, the propulsion device in petrol powered vehicles. This is a source of pollution, noise, expense and political problems.

Lead Acid Batteries. These are old technology batteries that are less expensive than that used in most of the world’s light electric vehicles. Even if they are heavy, they are very dependable. They also have excellent discharge and charge capabilities and almost 100% recyclable. They are also called SVRLA and Pb A or Pb batteries. They have a nominal voltage of 1.75V – 2.4V.

Low speed electric assisted bicycle. This is what the USA law calls an electric bicycle.

Max Discharge or Max Current. This refers to the discharge rate of the battery.

Manual bicycle. A bicycle propelled by human power only. It is a very old design like sails or manual typewriters or charcoal writing on slate.

Motor. An electric motor that assists the rider. It can be found in various places and styles of placement.

Pb or Pb A batteries. This refers to lead acid batteries.

Neodymium. This is a rare earth metal that is used for the production of high energy permanent magnets. These magnets can be found in LEV motors and are one of the reasons why electric bikes cost a lot.

Ni Cad. Nickel cadmium batteries that are not used for some time by electric bicycles but found on some older models. Toxic and lower in performance compared to Lithium and NiMH.

NiMH Battery. This is short for Nickel metal hydride battery. It is non-toxic, delivers better performance than lead acid but less than lithium. It is not quite common but still found in some e-bikes.

Pedelec. It is an electric bicycle where the rider has to pedal for the motor to run. Variants of this are the PAS design used in Japan, and the EPAC design used in Europe.

Permanent Magnet – It is a magnet that stays magnet that stays magnetized without external supplies of energy. They are used in almost all motors used on light electric vehicles.

Push to start or pedal to start. A few electric bikes need the user to pedal a few strokes or gain a certain level of speed by pedaling before the motor could be activated.

Speed Sensor. This is a device which detects the rate of pedaling and is used to activate power in pedelecs. It does not have a nice feel as a torque sensor system.

SOC. State of Charge is the gas gauge or how much useable energy is available in the battery. It seems to be a simple task but this could be important to user satisfaction and could be quite complicated to establish.

SVRLA. It stands for sealed valve regulated lead acid batteries and are the most common kind of electric bike and electric scooter battery at present.

Tire Scrubber or Friction Drive. It is a friction roller that rides against the vehicle tire and uses the outside diameter of the tire as a gear reduction as well as the point of power application. This is a very simple system that was the main design during the early days of electric bicycles.

User Interface. It is the interaction of the user and the machine that includes controls, pedals and seat but normally refers to the data display of information such as distance, SOC and speed. It has quickly become interactive with the internet and GPS through phone and other gadgets.

Wiring Harness or Harness. This refers to the wires, switches and connectors which carry electric current as well as signals about the vehicle.


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