What's All This Stuff on My Ebike? We Answer Your Component Questions Here

WIRED

08-08-2025

Short answer: There's a drivetrain on it! We go over the battery, sensors, and other components that make your electric bicycle go.
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An electric bicycle—it's a regular bicycle, but with a motor on it! There are enough moving pieces on these personal mobility vehicles to make buying one confusing. Even if you're pretty sure you know what an electric bicycle is —and that you're not, riding, say, an electric motorcycle from a dealership—the technology changes almost daily.
Over the past 10 years, battery capacity has increased by around 50 percent, according to Joe Buckley, the e-mountain bike product manager at Specialized. In addition to monster battery power, motors are also getting beefier. 'Motor power is a big topic right now and is viewed by many riders as one of the most important features when considering their purchase,' says Buckley.
Exciting developments are on the horizon, but no matter how ebikes evolve, one rule remains steadfast: Buy a bike from a manufacturer that offers good customer support. 'At some point your bike will need service,' says Buckley, 'and lack of support from the brand means more money from the rider and less time on the bike.'
Here are the five major parts of an electric bicycle's power system: battery, sensor, motor, display, and remote. For more information, check out our How to Buy an Electric Bike or How to Rent an Electric Bike guides.
The battery is the electric bike's proverbial gas—it powers the motor as well as auxiliary components like lights. Most ebikes use rechargeable lithium-ion (Li-ion) batteries. The best Li-ion batteries are characterized by their long lifespan, lighter weight, and higher energy density. The worst are poorly made, untested, and can be a fire hazard, so check the US Consumer Product Safety Commission's page on recent safety recalls and battery best practices, before buying an ebike.
For an excellent detailed explanation on how a Li-ion battery works, visit the US Department of Energy. The important takeaway on Li-ion batteries for electric bicycles is that they are measured by both their energy density and power density. The energy density, or the amount of energy a battery can store, is measured in watt-hours per kilogram (Wh/kg).
Power density is the amount of power that can be generated by the battery and is measured in watts per kilogram (W/kg). A good way to visualize the difference between the two is using the analogy of draining a swimming pool: Energy density equates to the size of the pool, while power density measures how quickly the pool can drain.
Two other vocabulary words that crop up regarding batteries are volts and amps (or amperes). Volts are the amount of electrical force or pressure the battery can produce, or the speed of the battery's output of current. Amps are the volume of electrons that are passing through the system, or a measurement of the strength of the battery's output.
While power density, volts, and amps all matter, the one to pay the most attention to is the Wh/kg measurement, because this is a reliable indicator of the ebike's range on one charge. The Wh/kg range from roughly 300 to 1,000, with a corresponding range from about 15 miles to upwards of 100 miles. But don't take these ballpark figures as gospel: An ebike's range depends on multiple factors including terrain, temperature, the rider's weight, the level of assistance the rider is using, how well maintained the bike is, and the tire pressure.
If the battery is the heart of the electric bike, sensors are the nerve tissues of the spinal cord that coordinate the reflex actions of the motor. Sensor configuration depends on the manufacturer, but they generally fall under three categories: Speed sensor: A speed sensor measures the bike's speed and talks to the motor so that it can shut off when it reaches the legally permitted maximum assisted speed, which is 20 mph on a Class I or II or 28 mph on a Class III ebike.
A speed sensor measures the bike's speed and talks to the motor so that it can shut off when it reaches the legally permitted maximum assisted speed, which is 20 mph on a Class I or II or 28 mph on a Class III ebike. Cadence sensor: When you start pedaling, the cadence sensor signals the motor to kick in, which it does with a short delay. When the rider stops pedaling, the motor stops. Simple and cost-efficient, cadence sensors provide consistent power no matter how much force the rider is exerting. Their top speed is governed by the power level the bike is in. Most ebikes have at least three levels of power ranging from—eco to trail to turbo mode. These power levels can be tweaked via the remote (normally in the form of an app) to further customize.
When you start pedaling, the cadence sensor signals the motor to kick in, which it does with a short delay. When the rider stops pedaling, the motor stops. Simple and cost-efficient, cadence sensors provide consistent power no matter how much force the rider is exerting. Their top speed is governed by the power level the bike is in. Most ebikes have at least three levels of power ranging from—eco to trail to turbo mode. These power levels can be tweaked via the remote (normally in the form of an app) to further customize. Torque sensor: A torque sensor measures the movement of the pedals, as well as the amount of force the rider is using to push them. Because it immediately responds to the cyclist's effort without delay, this sensor provides the most natural feeling ride.
If the battery is the heart, the sensor is the brains, then the motor is the muscle of an ebike. Ebikes have two kinds of motors: hub-based or mid-drive (what others might call crank-based). There are advantages and disadvantages to each.
A crank-based motor is integrated into the bike's frame, making it more expensive to design. But it also feels more natural to ride, like an analog bike. Hub-based motors, which are laced into the rear wheel, are generally less expensive because bike manufacturers do not have to engineer the frame around the motor. They are also generally less powerful on hilly terrain and can wear out more quickly. On the flip side, they are also easier to replace.
A motor's power output is measured by wattage: Most ebike motors range from 250 to 900 watts, the latter generally reserved for electric mountain bikes that are designed to climb thousands of feet per outing. Another measurement important to note is the motor's torque—the more torque, the more power and responsiveness you'll get from the motor. For example, the most powerful electric mountain bikes have north of 100 newton-meters of torque.
The display is the ebike's brain—tracking and displaying speed, distance, battery level, ride time, and even GPS navigation. More sophisticated bike computers even track elevation, cadence, power, and heart rate.
This small screen sits in the cockpit, often around the left brake shifter or on the top tube. An electric bike will also have buttons next to the shifters and gears that will let you control the bike, to add more or less assistance or even use turn signals with your lights.
Most ebikes also have corresponding apps downloadable to Android or iPhones that further calibrate and fine-tune the ride, customize the display, control walk assist, and keep track of and even remotely lock the bike. It can do almost everything but turn the pedals. You can also mount your phone to your bike to use as a display.
What is an electric bicycle?
An electric bike has two or three wheels and has a motor of under 750 watts.
'E-motos are often falsely advertised to consumers as electric bicycles, but they go faster than 20 mph with a throttle and/or they exceed the 750-watt limit required by federal regulations,' says Ash Lovell, vice president of government relations at People for Bikes. 'We've been working on this issue for the past few years, and we're excited to see that people are starting to better understand what is and is not an electric bicycle.'
How old do you have to be to ride an electric bike?
In many states, you must be over 16 to ride an electric bike, but you can check your laws by state here. Generally, we do not recommend an electric bike for anyone under the age of 16.
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