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What Are the Parts of an E-Bike?

Here’s a glossary of terms for the components of an electric bike.

E-Bike 101: An explanation of terms


The axle is at the very center of the hub. It is the threaded metal shaft around which the wheel rotates. It attaches to the fork of a bicycle by sliding into the dropouts, and remains stationary as the wheel turns.

See also: Quick Release Axle

Battery (Battery Pack):

We use the term “battery pack” to refer to the entire, completed battery unit. A fully-assembled battery pack is made up of a module, a controller, and the connectors needed to provide the power to your kit. All of Ukko’s batteries are Lithium-Ion.

See also Cell, BMS, Capacity (Ah), Voltage (V), Wattage (W)


“BMS” stands for “Battery Management System.” It is a chip that lives inside most battery modules and protects the battery against damage caused by over-draining or over-working the cells.

See also: Battery


Brakes, like those used in a car, are the mechanisms used to slow and/or stop the bicycle. Most brakes are controlled with levers located on the handlebars. The three most common types of brakes are rim brakes, disc brakes, and coaster brakes.

See also: Wheel, Hub, Rim

Cable Set (Harness):

Our kit comes with a cable set, also called a harness, that connects all of the components to each other. The set is made up of two separate cables that are connected at the battery. One of these cables runs from the battery to the grip switch or throttle that attaches to your handlebars. The other cable runs from the battery to the motor that serves as the hub of the front wheel.

See Also: Wheel, Controller

Capacity (Ah):

Every battery has a “capacity” which rates how much energy it can store. We measure our batteries in Amp-hours (Ah). For every Amp-hour in its rating, a battery can provide one Amp of current for one hour.

See also: Voltage (V), Wattage (W), Module


A cell is the smallest unit of energy storage in a battery. For example, one AA battery is a single cell. If a device calls for 4 AA batteries, all four of these cells will function together as one battery. Most large batteries are made up of multiple individual cells hooked to each other in either “series” (which combines the voltage (v) of the cells but not the capacity), or in “parallel” (which combines capacity, but not the voltage) or a combination of the two techniques. When all the cells have been hooked together, they are called a module.

See Also: Controller, BMS


A conventional bicycle is driven by the transferrence of force from the cranks to the rear wheel. The chain is the component that connects the cranks and the rear wheel, and transfers this energy.

See Also: Pedals, Drive Train


Our battery chargers are used to restore depleted power to the cells of our battery with power supplied from the wall. Other power sources are available such as power from a solar panel, provided that the proper inverter is used.

See also: Voltage (V), Wattage (W)

Coaster Brakes:

Coaster Brakes are one of the three most common types of bicycle brakes. Unlike other types of brakes, coaster brakes apply braking force to only the rear wheel. Instead of being controlled with a lever on the handlebars, the brakes are applied by putting reverse pressure on the pedals.

See Also: Rim Brakes, Disc Brakes, Hub, Drive Train, Cranks


The Controller is an important component of our battery packs. The controller is responsible for converting the raw energy coming from the module into the type of modulated current that’s needed to run the motor.The controller is also reponsible for shutting off the battery if the amount of energy being used is too high. This protects the cells from being damaged.

See Also: BMS, Capacity, Hub


The Cranks are an important part of the drive train of the bicycle. They hold the pedals; connecting them to the frame, and transferring the energy applied to the pedals into the chain.

See Also: wheel

Disc brakes:

Disc Brakes are one of the three most common types of bicycle brakes. Disc Brakes operate in a manner similar to many automobile brakes. When a lever on the handlebars, is applied, two brake shoes squeeze a rotor that is bolted to the hub of the wheel, thereby slowing or stopping the bike.

See Also: Rim Brakes, Coaster Brakes, Hub, Rim

Drive Train:

The Drive Train is the name given to the entire system of the bike that accepts energy from the rider, and converts it into forward motion. Energy enters the system through the pedals, and is transferred through the Cranks into the chain. The movement of the chain in turn moves the rear wheel, which pushes against the ground, and propels the bike forward.

See Also: Frame


“Dropout” is the name for the notches at the bottom of the fork into which the axle fits. Due to variations in production standardization, some forks will require you to file off the paint inside of the dropout for the slightly larger Hill Topper axle to fit.

See Also: Hub, Wheel, Motor


The fork is the piece at the front of the bike that holds the front wheel and attaches it to the frame. The fork combined with the handlebars is responsible for steering the bike.

See Also: Dropout, Axle


The frame is the tubing that connects and supports the components of the bicycle. A bicycle’s frame is largely responsible for rider posture, rider comfort, and the efficiency of the ride.

See Also: Fork, Dropout, Handlebars

Grip Switch:

“Grip Switch” is the name we use to refer to the button which activates the hub Motor. Not to be confused with the power switch, the grip switch attaches to your handlebars and is used to control whether or not your Hill Topper is providing assitance throughout the ride. The grip switch differs from a throttle, in that our grip switch is either on or off, but a throttle allows variation in power.

See Also: Cable Set, Hub


The handlebars are the brain of a standard bicycle; they provide the means for steering and balancing the bike. Handlebars also house the controls for the brakes, shifters, and any add-ons, like lights or cycling computers. The Hill Topper’s grip switch mounts on the handlebars, providing a convenient way to give yourself a boost of power when you want it.

See Also: Fork, Frame


A Hub is one of the two main components of a wheel, along with the rim. The hub is the center of the wheel, housing the bearings that allow the wheel to spin, and supporting the axle and the spokes. There are many different types of hubs, For example, the Hill Topper uses a motorized hub.

See Also: Disc Brakes, Dropout, Fork


“Mid-Drive” is the term used to describe a specific type of electric bikes and conversion kits. Whereas the Hill Topper is a Front Drive, because the energy is applied to the front wheel, a mid-drive system doesn’t supply power directly to either of the wheels. Mid-drive systems supply power into a bike’s drive train usually by way of the cranks. While there are some advantages to this type of system, they also tend to be more complex and difficult to install and service.

See Also: Motor, Chain, Pedals


The Module is the part of a battery pack that stores electricity. If a battery has more than one cell, then “module” is the term used to refer to all of the cells together. If a cell compares to a store room, then the module would compare to the whole warehouse.

See Also: Controller, BMS, Power Switch, Capacity


The Hill Topper Motor is located in the hub of the front wheel. The motorized hub spins freely when not engaged, just like a standard hub, but it can also pull the bike forward when it is activated. Our motors come in 24v 250W, or 36v 350W versions.

See Also: Battery, Mid-Drive


The nipples are the threaded metal sleeves that thread onto the ends of the spokes and anchor them through the holes in the rim. The nipples are the part of the wheel that are adjusted to manipulate the round and true of a wheel.

See Also: Hub, Axle, Tire


Pedals are one of the three “contact points” of a bicycle. the other two are the seat, or saddle, and the handlebars. The padals are the part of the bike where the rider places their feet, and the pedals received force from the the rider’s feet and transferrs that force into the cranks.

See Also: Drive Train, Chain

Power Switch:

Our batteries have a Power Switch. If a Hill Topper were to be compared to a car, our power switch would be like the car’s ignition, whereas our grip switch behaves more like a car’s gas pedal. Some people don’t bother to turn off their power switches, but it is an important part of taking care of your battery.

See Also: Charger, BMS, Battery

Quick release axle:

A “quick release” axle serves the same purpose as any other axle, i.e. serving as the center of the wheel, and attaching it to the frame. Whereas traditional axles are attached by tightening down bolts that are threaded onto the axle, Quick Release axles use a lever to achieve the necesarry tension needed to hold the wheel sucurely. The result is that the wheel can be removed without the need for any tools. Our Hill Topper wheels come standard with bolt-on axles, but we do have quick-release axles available for our 250W, 24v kits.

See Also: Hub, Fork, Dropout


The Rim of a wheel is the metal hoop that holds the tire. The rim is also responsible for transferring energy coming from the hub (through a chain-style drivetrain, or a hub motor) through the spokes, into the ground, propelling the bike forwards. The rim is the part of the wheel being manipulated when it is rounded or trued. Most hubs could be built into a wide range of wheel sizes, so it is the rim that determines the wheel’s size.

See Also: Nipples, Rim Brakes, Axle

Rim brakes:

Rim Brakes are the most common type of brakes for modern bicycles. They attach to the frame, and work by applying a squeezing pressure to the sidewalls of the rim when the brake levers are used.

See Also: Disc Brakes, Coaster Brakes, True, Tire, Wheel









Voltage (V):

Wattage (W):