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E-bike motor systems explained

Hub motors vs mid-drives, geared vs direct-drive hubs, torque vs cadence sensing, and how closed maker systems and open parts systems differ when something needs fixing.

Last edited Nov 9, 2026 by Pedalwise team Edit History Add a subpage

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Every e-bike has the same basic parts: a motor, a battery, a controller that decides how much power to send, sensors that tell the controller you are pedaling, and a display or remote. Who makes those parts, and how they are sold, decides what you can check at home, what a shop can fix, and where replacement parts come from. This page explains the main motor types and the two broad kinds of systems, then links to a page for each system.

How to tell which one you have

  • Look at where the motor sits. A mid-drive sits between the cranks at the bottom bracket. A hub motor is the large center of the front or rear wheel, with a cable leaving the axle.
  • Read the label on the motor. Makers print a model or article number on the housing. Bafang's mid motors carry codes that start with MM and its hub motors codes that start with RM (Bafang mid motors, Bafang hub motors). Specialized lists the label code for each of its motors (Specialized motors), and Brose tells riders to check the article number on the drive unit (Brose Mag manual).
  • Check the display and the app. Bosch, Shimano and Yamaha each make their own displays, and the app your manual names is a strong clue. Bosch's smart system uses the eBike Flow app, while Bosch eBike system 2 uses eBike Connect (Bosch overview).
  • Check the bike maker's parts page. Some direct-to-consumer brands built the same model with motors from different makers. Ride1Up's replacement wheel page lists a 500 Series (Shengyi) and a 500/700 Series (Bafang) version, among others, and asks owners to confirm their version before ordering (Ride1Up rear wheel and motor).

Hub motors and mid-drives

Hub motors

A hub motor turns the wheel itself. Electric Bike Report describes two kinds (hub motor guide):

  • Geared hubs use internal gears to turn the shell. They are usually smaller, lighter and cheaper, and better at climbing.
  • Direct-drive hubs have no gears. They are larger and heavier, but quiet and very long lasting, and work best at higher speeds.

Some geared hubs coast freely when the motor is off. For example, Grin notes that the Shengyi SX hubs it sells have a built-in clutch that freewheels with no drag when unpowered (Grin on Shengyi SX hubs).

What it means for repair: a flat on the motor wheel means unplugging the motor cable and refitting axle hardware in the right order, and the axle has to be held firmly in the dropouts. See fix a flat on a rear hub motor wheel, torque arm and hub motor troubleshooting.

Mid-drives

A mid-drive turns the chainring, so its power runs through your chain and gears, and it can use the bike's gears on climbs. Most of the closed systems below are mid-drives, such as the Bosch Performance Line CX, the Shimano EP8 family, the Yamaha PW series and the Brose Drive S. Because the motor's effort goes through the drivetrain too, keep an eye on chain wear. See check and replace a chain and clean and lube a chain.

Torque and cadence sensing

  • Cadence sensors detect that you are pedaling and how fast, then give a set amount of help for the assist level. Aventon says they are simpler, which tends to make repairs easier (Aventon on sensors).
  • Torque sensors measure how hard you push and match the help to your effort, which feels more natural. Aventon notes they can need more complex repairs.

A torque sensor reads your foot pressure when the system starts. Shimano says that if it was set while you pressed on the pedals, assist can feel weak, and the fix is to switch off and back on with your feet off the pedals (Shimano assist checks). See pedal assist sensor and no pedal assist.

Closed maker systems

Bosch, Shimano, Yamaha, Brose and Specialized sell matched sets of motor, battery, display and software, and so do Fazua, TQ and Giant. What that means for repair:

  • Dealer software does the deep work. Bosch dealers use the DiagnosticTool to update the bike, make adjustments and produce a diagnosis report (Bosch dealer service). Shimano's phone app, E-TUBE PROJECT Cyclist, shows errors and changes settings, while firmware updates and Service Reports use the PC version, E-TUBE PROJECT Professional (Shimano FAQ).
  • Parts work only inside their own system. Tern explains that Bosch smart system and Bosch eBike system 2 parts, batteries and chargers included, only work with their own system (Tern on Bosch systems).
  • The drive unit stays closed. Brose's manual says never to open the drive unit and that unauthorised opening voids the warranty (Brose Mag manual).
  • The upside is published error codes, a dealer network and a clear warranty path.

Open parts systems

Most direct-to-consumer and kit bikes use motors from parts makers such as Bafang, Shengyi, Dapu, MXUS and Aikema, all covered in Electric Bike Report's guide (hub motor guide). The bike maker picks a motor, controller, display and sensors and puts them together. What that means for repair:

  • Parts are sold as units. Ride1Up sells a full rear wheel or a motor on its own, and separate 500 Series controllers for its Bafang and Shengyi versions (Ride1Up rear wheel, Ride1Up 500 Series parts).
  • Parts must match. Grin warns that Shengyi's hall sensor wiring order differs from Bafang's, so a controller made for Bafang may not work straight away (Grin on Shengyi SX hubs). Bafang moved its parts from the older UART link to CAN bus, which work in different ways (Bafang on CAN and UART). Bafang also names poor matching of motor and controller as the main cause of electrical motor noise (Bafang FAQ).
  • Diagnostics depend on the maker. Bafang's BESST tool handles diagnosis and updates, and dealers get access through the bike brand (Bafang BESST).
  • Error codes come from the display. The same number can mean different things on different displays, so look up your display's own manual. See e-bike error codes.

Whatever the system, never open a motor, battery or controller, and never change speed or power limits. Wiring and battery faults belong with a shop. See when to call a pro and e-bike battery care.

Systems on Pedalwise

Videos

Hub Motor vs Mid-Drive: What a Bike Mechanic Would Buy from RIDE eMTB: A mechanic weighs hub motors against mid-drives, covering how each one drives the bike and what each costs to keep running.
Ebike Power Delivery Explained: Cadence vs Torque, Hub vs Mid Drive from Chris Crossed: Explains cadence and torque sensors and how they change the way assist comes on, alongside where the motor sits.
A closer look at the upgraded EP Series e-bike system: SHIMANO from #RideShimano: Shimano's own look at one complete mid-drive system, showing how the motor, battery, display and app work together.

Related pages

Sources

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