What Is an E-Bike? How It Works and the Classes 2027

What is an e-bike and how does it work? An e-bike is a bicycle with an electric motor and a rechargeable battery. A controller reads sensors on the bike and tells the motor how much to help, so on most e-bikes the motor adds power while you pedal. In the United States, e-bikes are also sorted into Class 1, Class 2 and Class 3 by whether they have a throttle and how fast the motor helps, and "Class 4" is not an official class in the sources I found.

I haven't ridden or tested the e-bikes in these sources. The explanations come from Levy, Batoo Bike, the Electric Bike Company and Biketips (companies and a review site), Wikipedia, and three legal sources: a U.S. federal statute, a National Conference of State Legislatures (NCSL) primer and California's vehicle code. Some company pages are unsourced, and I mark where they disagree. Laws change and vary by state, so this is general information and not legal advice. If you searched what is an ebike and how does it work, the first paragraph is the short version.

This page may contain affiliate links, which means ElectricMood can earn a commission if you buy through them. See the affiliate disclosure. If you are ready to shop, my best electric bikes guide compares them.

What is an e-bike?#

Wikipedia defines an e-bike as "a type of a motorized bicycle with an integrated electric motor used to assist propulsion." It separates two kinds: pedelecs, where the motor assists only while you pedal, and throttle or power-on-demand bikes, where you engage the motor by hand, usually from a handlebar grip. (The throttle description on that page is uncited.)

U.S. federal law has its own definition. Under 15 U.S.C. 2085, a "low-speed electric bicycle" is a two- or three-wheeled vehicle with fully operable pedals and an electric motor of less than 750 watts (1 horsepower), whose maximum speed on a paved level surface, powered solely by the motor and ridden by someone weighing 170 pounds, is less than 20 mph. The Consumer Product Safety Commission regulates these as consumer products.

For why people ride them, see my what is the point of an e-bike and electric bike advantages and disadvantages guides.

How does an electric bike work?#

How does an electric bike work? The sources describe the same four parts, with different levels of detail:

• Motor. Levy says there are hub motors, built into the front or rear wheel, and mid-drive motors, mounted near the cranks. The Electric Bike Company says the motor supports pedaling rather than replacing it.
• Battery. The Electric Bike Company calls it a rechargeable pack, usually on the frame. Levy calls lithium-ion "the most common" and Wikipedia says most e-bikes now use lithium-ion polymer batteries (uncited). Batoo says capacity is given in watt-hours (Wh), which determines range, and that the battery includes protective electronics and is usually removable.
• Controller. Levy says it "regulates the power flow from the battery to the motor based on the rider's input." The Electric Bike Company says it receives signals from the pedal sensors and decides how much help to add.
• Sensors and display. Batoo says sensors measure cadence and/or torque at the pedals, plus wheel speed. A handlebar display lets you choose the assist level (Levy).

In practice, you pedal, the sensors tell the controller, and the controller sends power from the battery to the motor. Batoo says assistance is "only triggered if you pedal," and that the bike is built to feel like a regular bicycle. Batoo also says the bike stays rideable with a dead or removed battery, but is heavier to start and climb with. Recharging while pedaling is described as negligible, and the Electric Bike Company says regenerative braking, where the motor acts as a generator, is optional.

Hub motor, mid-drive and sensor types#

Hub versus mid-drive, per Batoo (a seller): a mid-drive motor sits at the bottom bracket and feeds the transmission, and is described as offering higher torque, better balance and often a more precise torque sensor. A hub motor sits in the front or rear wheel and is described as simpler, often lighter and cheaper, with lower maximum torque on steep slopes. Biketips (reader-supported, with affiliate links) says rear hubs are far more common because a front hub affects handling more.

Cadence versus torque sensors, per Biketips: torque sensors sit in the pedals, cranks or chainset and measure how hard you push, and are mainly linked to mid-drives, while cadence sensors measure how fast the pedals turn, and hub motors usually use them. It says hub motors deliver more constant assistance and respond less to your effort. Wikipedia notes torque sensors were developed in the late 1990s and that 2020s bikes feature them. Levy and the Electric Bike Company say the system detects pedaling effort without naming a sensor type.

These are general descriptions from sellers and not tests. If you want to know which your bike has, the manual or spec sheet will say.

Power, range and battery size#

Levy says motor power usually ranges from 250 W to 750 W in most consumer e-bikes and range from 15 to 50 miles per charge, both unsourced. Wikipedia says batteries typically last 40 km (25 mi) to 120 km (75 mi) per charge, cited, and that range depends on assist level, battery capacity, speed, terrain and rider and bike weight (the factors are uncited). Biketips gives typical specs of a 250 W to 750 W motor and a 36 V to 48 V battery of 10 to 21 amp-hours, though its own body later says 350 to 500 W, so that page is inconsistent. Mid-drive power is said to be typically limited to about 250 to 500 W (Wikipedia, with a citation-needed tag).

My reading: the sources agree on "a few hundred watts, a few hundred watt-hours" for a normal e-bike, and disagree on the details. For speeds, see my how fast e-bikes go and fastest e-bikes guides.

What are the different classes of e-bikes?#

What are the different classes of e-bikes in the U.S.? Under the three-class system that NCSL's primer describes (26 states, per its 2021 update):

California's vehicle code (section 312.5) defines an electric bicycle as one with fully operable pedals and a motor that does not exceed 750 watts, then describes the three classes the same way: Class 1 "low-speed pedal-assisted," Class 2 "low-speed throttle-assisted," and Class 3 "speed pedal-assisted" with a speedometer. NCSL says the 750 W figure comes from the federal definition rather than the classes, and that all 26 states using the system require a label showing the class number, top assisted speed and motor wattage.

States vary. NCSL says New Jersey uses a different two-tier system and requires registration, a license, insurance and a helmet for bikes that assist above 20 mph, and that West Virginia recognizes Class 1 and 3 but not Class 2. Connecticut is the strictest on helmets, per NCSL. NCSL's primer dates from 2021, and Radmoto (a retailer) says New Jersey and Connecticut changed their rules in 2026 and California issued a consumer alert in April 2026. I haven't verified those, and my e-bike laws by state guide covers them. For where you can ride, see my guides to the road and the sidewalk.

What is a Class 1 e-bike?#

What is a class 1 e-bike? A Class 1 e-bike gives motor help only while you pedal, with no throttle that can move the bike on its own, and the help stops at 20 mph. That is the wording in both NCSL's primer and California's code. Rider Guide says Class 1 motors typically range from 250 W to 500 W. Upway (an e-bike seller) says Class 1 or 2 is right for most seniors because "the goal is confidence, not speed."

If you are wondering what is a class 1 electric bike compared with the others, it is the pedal-assist-only bike with the lowest top assisted speed of the pedal-assist classes. Rider Guide says Classes 1 to 3 are generally allowed in bike lanes and on most bike paths and trails, with exceptions such as designated mountain-biking trails. Check local rules before you ride.

What is a Class 2 e-bike?#

What is a class 2 e-bike? A Class 2 e-bike has a throttle that can move the bike without pedaling, and the motor stops assisting at 20 mph (NCSL and California's code). Urtopia (a maker) says a bike with a throttle that moves without pedaling is a Class 2 in the U.S. Many Class 2 bikes also have pedal assist, but the class comes from the throttle.

EVELO (a seller) says to treat the throttle like a car's gas pedal. At 20 mph the motor stops adding power. My reading, as opinion, is that you can still pedal faster than that on your own.

What is considered a Class 3 e-bike?#

What is considered a class 3 ebike? A Class 3 e-bike gives motor help only while you pedal, and the help stops at 28 mph. California's code requires a speedometer, and NCSL says the same. Several states require helmets for all Class 3 riders regardless of age, per NCSL. NCSL says West Virginia doesn't recognize Class 2, and Radmoto says Massachusetts doesn't recognize Class 3.

Sources conflict here. Rider Guide's class article describes Class 3 as "controlled by a throttle." NCSL and California's code say Class 3 is pedal assist only, with no motor-only propulsion, so I'd trust the statutes over that summary. If you want to know how fast e-bikes go, see my e-bike speed guide and how fast they go without pedaling.

What is a Class 4 e-bike?#

What is a class 4 ebike? I found no official Class 4 in the NCSL primer or California's code. Radmoto (a retailer) says an early version of a Rhode Island bill proposed a "Class 4" for bikes over 750 W and 28 mph, and that the proposal was removed. Rider Guide says Class 4 bikes are "generally classed as off-road electric bikes" that "fall under the same restrictions as dirt bikes." Both are secondary sources, and neither gives a statute.

Radmoto describes high-power electric dirt bikes, which it calls e-motos, as machines that "typically produce thousands or tens of thousands of watts" and says they are harder to call bicycles. It also says motors are often sold as "750 W rated" while peak output can be much higher, so check the manufacturer's class label. And it says modifying a bike beyond its class limits can change its legal classification. My view, as opinion: if a seller calls something a Class 4 e-bike, ask what law it is meant to fit, because the three-class system does not include it. NCSL says devices outside the definitions may be regulated as other vehicles. For the on-road side, see my road legality guide.

Which class is right for you?#

Opinion, built on the sources: Class 1 is the simplest and the most widely allowed on paths, Class 2 adds the throttle, and Class 3 is faster and brings more rules. Check the class label on the bike, check your state's rules, and read my what to look for in an electric bike guide for the rest of the buying checklist. If you have a hybrid in mind, see what is a hybrid electric bike.

Frequently asked questions#

What is an e-bike and how does it work?#

A bicycle with a motor, battery, controller and sensors. The controller tells the motor how much help to give based on what the sensors detect, usually while you pedal.

How does an electric bike work without pedaling?#

Only if it has a throttle. NCSL describes Class 2 as the class where the motor may propel the bike exclusively.

What is an ebike and how does it work compared with a moped?#

I found no source comparing them. Federal law sets low-speed e-bikes at under 750 W with fully operable pedals; other devices may be regulated as other vehicles (NCSL).

How does an electric bike work with a dead battery?#

Batoo says it is still rideable but heavier to start and climb with.

What is a Class 1 e-bike?#

Pedal assist only, with help stopping at 20 mph.

What is a Class 1 electric bike's top speed?#

The motor stops helping at 20 mph (NCSL, California). You can pedal faster.

What is a Class 2 e-bike?#

A bike with a throttle that can move it without pedaling, with motor help stopping at 20 mph.

What is considered a Class 3 ebike?#

Pedal assist only, stopping at 28 mph, with a speedometer required in California.

What are the different classes of e-bikes?#

Class 1, 2 and 3 in the states that use the three-class system (26 per NCSL's 2021 primer). Some states differ.

What is a Class 4 ebike?#

Not an official class in the sources I found. Sellers use the term for faster or off-road bikes.

Do I need a license for a Class 3 e-bike?#

NCSL says three-tier states typically exempt e-bikes from registration, licensure and insurance, but rules vary and New Jersey differs.

Where is the class label?#

NCSL says the 26 three-class states require a label showing the class number, top assisted speed and motor wattage.

The bottom line#

What is an e-bike and how does it work: a pedal-assisted bicycle with a motor, battery, controller and sensors. The classes are Class 1 (pedal assist to 20 mph), Class 2 (throttle to 20 mph) and Class 3 (pedal assist to 28 mph, with a speedometer), and Class 4 is not an official class in what I found. Rules vary by state, so check yours, and see my best electric bikes guide for specific bikes.

Written by Paul Gendry. Last checked October 10, 2026. Laws change, so check your state. This is general information, not legal advice.