Guide to e-bike components

covering motors, batteries, brakes, gears etc

If you've read our guide to e-bikes then you probably already know the style of e-bike you're looking for. This guide covers the various components that are found on a typical e-bike, and we also explain what to look for when comparing all those W, Ah, and V figures and what they mean in the real world.

The two main components on e-bikes are the motor and the battery. But that's not all you should be focusing on when making your buying decisions.

Motors

There are two types of motor found on e-bikes, crank motors and hub motors.

Crank motors (sometimes called mid motors) are located at the bike's bottom bracket (the area where the pedals are located). Crank motors are easy to spot due to the size of the units.

Yamaha Crank Motor

E-bike hub motor

Pros & Cons of Front vs Rear Hub Motors

Hub motors located in the front wheel will have the effect of "pulling" the bike along while rear hub motors will "push" the bike.

Rear hub motors provide a riding sensation more closely to that of a traditional bicycle.

Some riders find the unnatural "pulling" sensation of front hub motors unnerving.

Battery

Obviously e-bikes require a battery to power the motor. The batteries used in e-bikes are lithium-ion as found in electric cars. We've put together a detailed page on micromobility batteries and how to look after them on the link below.

For more information on batteries and how to look after them visit this page


Batteries are the heaviest component on e-bikes and on more modern bikes they are built into the frame making the bike hard to recognise as an e-bike compared to the e-bikes with the battery mounted to the frame itself.

e-bike batteries

Torque & Cadence Sensors

We now move on to the more technical areas in how power is delivered to the motor. While it may not be the most exciting of reads this area is rather important as it effects the quality of the ride.

The cadence sensor (sometimes called a pedal assist sensor) or torque sensor is used to determine the power that's delivered from the motor.

Cadence sensors are more basic and are found on e-bikes at the budget end of the market. Cadence sensors detect when there is pedal movement by using a series of magnets on the crank arm. The sensor determines the pedalling speed and delivers the power according to the manufacturer's setting for that cadence and the assist level setting. However the supplied power may not always be enough to maintain the same speed - for example when going up hills. The rider would then need to adjust the assist level setting to maintain the same speed.

Cadence Sensor

Torque Sensors

A torque sensor measures how hard the rider is pedalling or how much force is being put through the pedals. This is then used to determine how much power to provide to the motor. As torque sensors are constantly monitoring the pedalling force the power levels are continually adjusted based on the assist level setting. This then provides a more natural riding experience.

Let's compare the two sensor types for when riding up a hill. With a cadence sensor the rider will receive the same power going up a hill as when riding on the flats. To compensate for the drop in speed the rider can adjust the assist level setting to gain more assistance.

With a torque sensor however as the sensor detects the rider is working harder it will provide more power - thus smoothing out the ride.

Torque Sensor

E-bike Controller

The controller is the brains unit of an e-bike or electric scooter. Its role is make all the electrical components work together, (battery, motor, sensor, display, cut off brake lever). Think of the controller as being similar to your car's ECU (electrical/engine control unit).

The controller will take signals from the motor, pedal assist sensor and LCD display, and together with feedback from the rider through their pedal action and display settings will provide variable power to the motor.

On older e-bikes the controller is often housed under the battery, just behind the bottom bracket.

On newer bikes you won't be able to get access to the controller - but it's there and it's useful to have a basic understanding on what it does.

E-bike controller unit

Basic Explanation on Electrical Units found on e-bike specification guides

Amps (A)
Unit for measuring Current or rate of flow. Amount of power flowing through the system.

Volts (V)
Volts is the "force" or "pressure" pushing the Amps through the system. The more volts available the faster the energy can be delivered to the motor. A bike with a higher voltage can deliver more torque for faster acceleration but at a cost of faster battery drain.

Watts (W)
Electric power is measured in Watts. If you know the Voltage and Amps then you can calculate the Watts.

W = V x A

Amp-hours (Ah)
Measure of a batteries capacity. It’s a measure of how much current the battery can deliver in one hour. So a 10Ah, 36V battery will provide 10 amps for 1hr at 36V.

Watt-hours (Wh)
Wh = V x Ah
Watt hours (Wh) is probably the most useful rating - even though it's widely omitted from specification tables as it provides an indication as to how long the battery will last.

Watt hours is the number of watts that can be delivered in 1hr. So a 10Ah, 36V battery would give you 360Wh. If you paired that with a 350W motor and ran it non-stop you’d get about an hour of use.


So what do I need to look for when comparing specifications?
With e-bikes what we really want is a decent range, or how long will the bike run before the battery is flat. As a guide to this look for the Wh figure (or calculate the Wh figure) and the larger the figure the better.

E-bike size guide & frame geometry

bike frame measurements

 

Frames and bikes often come in a number of sizes and in order to find the most suitable fit you will may need to know your height and inside leg (inseam) measurements. You can then reference these details against the manufacturer's specification tables to find the ideal sized frame.

 

How to measure height
Take your shoes off and stand upright, with legs together against a wall. Keep your back straight and keep your shoulders back against the wall (no slouching). Carefully mark the wall at the top of your head - this is a lot easier with some assistance. Then measure the vertical distance from the floor to the mark.

rider height diagram

How to measure inside leg (inseam) measurement
Take your shoes off and stand upright with your back against the a wall. Place a book between your legs, level with your crouch (stop sniggering) and either mark the top of the book against the wall, making sure the book is kept horizontal or ask a friend (a very good friend) to measure from the floor to the top of the book. 

rider inside leg diagram
Once you have these measurements use the manufacturer's specification guide to find the correct frame size. If you're between sizes then it's best practice to order the smaller size as you can always increase reach with a longer stem and increase saddle height for additional leg clearance.

Frame and bike geometry terms
The diagram below references the terminology used when looking at a frame or bike's geometry. When sizing frames it's normally the "seat tube" length and/or "top tube" lengths that are quoted. Sizes can be quoted in cm, mm or simply S, M, L depending on manufacturer.
bike frame measurements
Wheel size: Size of wheel, follows various industry standard sizes
Seat tube size: Distance from centre of bottom bracket to top of seat tube
Seat tube angle: Angle of seat tube from vertical
Head tube length: Distance from top to bottom of head tube
Head angle: Angle of head tube from vertical
Top tube: Distance of actual top tube
Effective Top tube: Effective horizontal distance of top tube if angled
Bottom bracket height: Height of bottom bracket from ground
Bottom bracket drop: Vertical distance from centre of bottom bracket to axles
Chainstay: Length of chainstay
Fork offset: Distance front axle is offset from centre of fork
Stem extension: Length of stem. Measured from centre of handle bars to centre of head tube
Wheelbase: Distance from front to rear axles
Stand over: Vertical distance from ground to top of top tube
Frame reach: Horizontal distance from centre of bottom bracket to centre of head tube