E-Bikes 101: How They Work and What the Law Calls Them

The parts

Five Parts Turn a Bicycle Into an E-Bike

A motor drives the wheel or the cranks, a battery feeds it, a sensor reads the rider, a controller sets the power, and a display or app lets the rider pick an assist level.

Drive systems

Mid-Drives Use the Bike's Gears, Hub Motors Push the Wheel Directly

A hub motor sits in the front or rear wheel and turns it directly. It is cheap, quiet and independent of the chain, so it dominates direct-to-consumer commuter and fat-tire bikes from Rad Power Bikes, Aventon and Lectric, with hubs from Bafang, Ananda and other Chinese makers. Mahle's X20 is a light rear hub for road bikes.

A mid-drive sits at the bottom bracket and drives the cranks, so the motor works through the bike's gears and climbs steep grades efficiently. Mountain, cargo and premium city bikes use mid-drives from Bosch, Shimano, Yamaha, Brose, Bafang, Ananda, DJI and TQ.

A cadence sensor switches assist on when the cranks turn, so power arrives the same whether the rider pushes hard or soft. A torque sensor measures how hard the rider pushes and adds power in proportion, which feels like stronger legs. Torque, in newton-meters (Nm), measures the motor's twisting force at the cranks and sets how hard a drive pulls on a climb.

A throttle gives power with no pedaling. US Class 2 bikes may have one up to 20 mph. EU and UK pedelecs may not, apart from a walk-assist mode limited to 6 km/h.

The Drive Systems hub covers each maker in depth.

Legal classes

Assist Speed and Motor Power Decide Whether a Vehicle Is an E-Bike or a Moped

US federal law sets a ceiling of 750 W and 20 mph on motor power alone, and most states add the three-class system. The EU, UK and China cap assist at 25 km/h.

In the US, a bike sold over 750 W or able to exceed 28 mph on assist falls outside every class and becomes a moped or motorcycle under state law. China's GB 17761-2024 took effect on September 1, 2025, dropped the pedal requirement, limited plastics to 5.5% of vehicle mass and requires Beidou positioning on commercial-fleet bikes; only compliant bikes could be sold from December 1, 2025. The Laws hub covers each state and country.

Battery and range

Watt-Hours Set Range, and Certification Sets Fire Safety

A pack's energy is its nominal voltage times its amp-hours: a 36 V, 14 Ah pack holds 504 Wh, and a 48 V, 15 Ah pack holds 720 Wh. Most e-bike packs hold 400 to 900 Wh. A 36 V pack strings 10 cells in series and a 48 V pack strings 13. The cells come from Samsung SDI and LG Energy Solution in South Korea, Panasonic in Japan, Molicel in Taiwan, and EVE Energy and BAK Battery in China.

Range is energy divided by consumption. Gentle riding in low assist uses about 7 Wh/km; full assist on steep trails can reach 15 Wh/km or more.

UL 2849 certifies the whole e-bike electrical system and UL 2271 the battery pack in the US and Canada; New York City requires them under Local Law 39 of 2023, and a CPSC rule on micromobility lithium-ion batteries followed in June 2026. In the EU and UK, EN 15194 covers the e-bike and EN 50604-1 the battery. China's GB 43854-2024 covers e-bike lithium packs up to 60 V. The Batteries & Safety hub covers cells, charging and fires.

Body types

Frame Shape and Drive Follow the Job the Bike Does

The Types hub covers each style and the neighboring scooter and moped classes.

Market size

China Rides 380 Million Electric Two-Wheelers, Far More Than Any Other Market

China's figure counts every electric two-wheeler, including pedal-less scooters from Yadea, Aima, Tailg and NIU that qualify as electric bicycles under GB 17761. Europe makes most of the e-bikes it sells, and the US imports nearly all of its own, mostly from China.

In this section

Reference Pages and the Four Pillar Hubs