E-Bike Drive Systems

Motor position

Mid-Drives Turn the Cranks, Hub Motors Turn the Wheel

Where the motor sits decides whether it can use the bike's gears.

A mid-drive sits at the bottom bracket and drives the chainring, so its output passes through the bike's gears the same way the rider's legs do. Low gears multiply its torque on climbs, and high gears let it hold speed on flats. Every flagship in the table below except the Mahle X20 is a mid-drive.

A hub motor is built into the wheel hub and drives the wheel directly, so it sees one fixed ratio regardless of gear. A rear hub, like the Mahle X20 or the Bafang hub motors fitted to many Chinese and European commuter bikes, pushes from behind and feels closest to pedaling. A front hub pulls from the front wheel, leaves the rear drivetrain untouched and is the simplest to fit, but it can lose traction on loose climbs. Hub motors come geared, with a planetary reduction inside, or direct-drive, which is heavier but silent and able to recover some energy under braking.

Hub motor torque is measured at the wheel, so it does not compare directly with crank torque. Mahle rates the X20 at 23 Nm at the wheel and calls that comparable to a 55 Nm mid-drive.

Sensing

Torque Sensors Match the Rider, Cadence Sensors Only Detect Pedaling

A torque sensor measures how hard the rider presses on the pedals, usually with strain gauges on the crank spindle, and the controller adds assistance in proportion. Push harder and the motor pushes harder. Bosch, Shimano, Yamaha, DJI Avinox, TQ and the Bafang M510 all use torque sensing, and it is standard on mid-drives.

A cadence sensor uses a magnet ring to detect that the cranks are turning and switches the motor on at a set power for the chosen assist level, whatever the rider's effort. It is cheaper and common on hub-motor commuters and conversion kits such as the Bafang BBSHD. Riders feel it as a surge that starts a moment after the first pedal stroke.

Most current drives also read wheel speed and cut assistance at the legal limit: 25 km/h in the EU and 20 or 28 mph in the US, depending on class.

Gearbox and shifting

Drives Now Shift Gears for the Rider

Because the controller already knows speed, cadence and rider torque, drive makers have started choosing the gear too. Shimano's EP801 works with XT Di2 for Auto Shift, which picks gears by speed and cadence with manual override, and Free Shift, which changes gear while the rider coasts by turning the chainring with the motor. SRAM's Eagle Powertrain pairs a drive unit with an electronic derailleur that shifts automatically. Bosch links its drives to Shimano Di2 and to the Enviolo stepless hub for automatic shifting.

Pinion of Germany went further with the MGU E1.12, a 12-speed gearbox and an 85 Nm motor in one sealed unit at the bottom bracket, which removes the derailleur and cassette entirely.

Flagship drive units

Twelve Flagship Drives From Germany, Japan, China, Taiwan and the US

Torque and weight are maker claims for the drive unit alone. A dash means the figure was not confirmed.

Bosch raised the standard Performance Line CX from 85 Nm to 100 Nm and 750 W peak with its 2025 update. DJI's Avinox M2 sibling makes 125 Nm and 1,100 W. Specialized's standard 3.1 makes 101 Nm and the S-Works version reaches 111 Nm through firmware on identical hardware. Yamaha's lighter PW-XM gives the same 85 Nm as the PW-X3 at 2.6 kg. Independent dyno tests by BIKE Magazin and PT Labs measured the TQ HPR50 at about 38 Nm, below its 50 Nm claim.

Market structure

A Few Drive Makers Power Hundreds of Bike Brands

Most e-bike brands design frames and buy the motor, battery, display and controller as one system from a drive maker. The drive decides the bike's power, ride feel, app and dealer service network, so two bikes from different brands with the same Bosch Performance Line CX ride much alike. Trek, for example, fits Bosch drives across much of its range and the TQ HPR50 on its lightweight Fuel EXe. Orbea builds the Rise around the Shimano EP801.

A few large bike companies brand their own drive but buy the hardware: Giant's SyncDrive units are built by Yamaha, and Specialized designs its motors and has them manufactured by Brose. DJI launched Avinox through Amflow, a bike brand it backs, before selling the drive to other makers.

The supplier list is consolidating. Yamaha bought Brose's e-bike drive business in 2025, adding Brose's Berlin development team of about 110 people to its European subsidiary. Porsche announced in May 2026 that it was closing Porsche eBike Performance and the Fazua brand it had owned since 2022, with spare parts and service promised for existing riders. Chinese makers are moving the other way: Bafang supplies hub and mid-drive motors worldwide, Ananda builds drives in China and Vietnam with a European office in Arnhem, and DJI entered in 2024 with the highest torque on the market.

Conversion kits

Conversion Kits Add a Motor to an Ordinary Bicycle

A conversion kit fits a motor, controller, sensor and battery to a pedal bike. Mid-drive kits such as the Bafang BBSHD replace the bottom bracket and drive the chainring; the BBSHD is rated at 1,000 W and uses cadence sensing, so a bike built with it exceeds the 750 W limit for a US Class 1-3 e-bike and the 250 W EU pedelec limit. Hub kits replace the front or rear wheel with a motorized one and are the simplest to install. Kits come with no frame testing for the added load, and the finished bike's legal class depends on the motor rating and speed cutoff the builder sets.

Connected drives

Drive Controllers Now Run Apps, Locks and Rider Assistance

Current drives connect to a phone app for assist tuning, firmware updates and navigation, and Bosch's eBike Flow app adds an electronic lock and theft alarm. The same sensors that read speed, cadence and torque are the base for rider assistance such as ABS braking, radar alerts and automatic assist modes. E-Bikes and Autonomy covers where that is heading.

In this section

Drive Maker Pages