E-bike mid-drive motors

An e-bike with a mid-drive motor (also called a mid-drive e-bike or mid-motor e-bike) has the motor low in the frame, at the bottom bracket. So the power goes straight to the chain or belt, rather than into the front or rear wheel.

How it differs from a front-wheel or rear-wheel motor

• Front-wheel motor

  • Pulls you forward.

  • Can feel a bit like riding a scooter.

  • Slightly cheaper, often found on older or simpler models.

• Rear-wheel motor

  • Pushes you forward.

  • Quiet and powerful on sportier e-bikes.

  • Less convenient when the rear wheel or gears need maintenance.

• Mid-drive motor

  • Sits low and central, which makes the steering more stable.

  • Uses your gears, so it has plenty of torque at low speed.

  • Well suited to hills and headwinds, and to intensive daily use.

That is why most new e-bikes with a mid-drive motor are sold in the higher segment: city bikes, women's e-bikes with a mid-drive motor, touring bikes and trekking models.

Well-known mid-drive systems

Terms such as Bosch mid-drive motor, Bafang mid-drive motor, Shimano Steps, Yamaha and Brose all refer to the motor system, not to the brand of the bike itself.

• Bosch mid-drive motor: widely used on Gazelle, Batavus and Sparta, among others.

• Bafang mid-drive motor: often on sporty e-bikes and conversion kits.

• Shimano Steps / EP series: common on city and trekking bikes.

• Yamaha / Brose: found on sporty models and speed pedelecs, among others.

Good to know: you can have a Gazelle e-bike with a mid-drive motor and a Bosch system, but also a Sparta or a Batavus with exactly the same motor system.

The motor is only half the story. On an e-bike with a mid-drive motor the battery determines how many kilometres you get, how long the system lasts and how safe it all stays.

Why a mid-drive motor asks more of the battery

A mid-drive motor:

• delivers high torque (a lot of force) at low speed;

• is often used in the high assistance modes (Sport/Turbo);

• draws a lot of current when you have:

  • hills or bridges to climb,

  • a headwind,

  • heavily loaded panniers or child seats.

The result: the battery regularly has to deliver high peak currents. That is not a problem if the battery is well designed and you treat it properly, but it does mean that:

• wear shows sooner (less range);

• weak cells come to light earlier;

• faults in the battery pack or the BMS (Battery Management System) show up more clearly.

1. Number of charge cycles Every battery has a limited number of full charge and discharge cycles.

2. Riding mode

   • A lot of Turbo/Sport = more comfort, but more wear too.

   • More Eco = easier on the battery and a longer range.

3. Temperature

   • Below about 10 °C the capacity drops temporarily.

   • A lot of heat (in full sun or near a heater) speeds up permanent ageing.

4. Storage

   • Preferably do not put the battery away completely full or completely empty.

   • A charge of around 40 to 60% in a dry, cool place is ideal.

5. Load

   • Daily use with a lot of kilometres (couriers, commuters).

   • Heavy loads (trailer, child seats) on high assistance.

• Use Eco or Tour as your default mode and only switch to Turbo when you really need it.

• Do not charge from 0 to 100% every time. Short top-ups between 30 and 80% are better.

• Avoid parking for long periods with a full battery in a hot shed or car.

• Check the battery and charger regularly for damage, melted spots or unusual smells.

With mid-drive bikes we see the same complaints again and again in practice. Some are in the motor, some in the battery, and sometimes the cause is in the wiring or electronics between the two.

1. Range drops quickly

What you notice:

• You used to get 80 km, now only 30 to 40 km.

• The battery runs down fast, especially on higher assistance.

• The indicator on the display drops in one go from half full to nearly empty.

Possible causes:

• Natural ageing: the cells are past their best.

• One or more weak cells in the pack.

• Incorrect storage (put away empty or full for a long time).

• Imbalance between the battery cells.

What KWS Seuren can do:

• A capacity test and safety check during the intake test.

• Advice: a new battery or a battery cell replacement (cells replaced with equivalent or better ones).

• A check of the BMS and the temperature protection.

2. The mid-drive e-bike cuts out or no longer starts up

Complaints:

• The bike no longer switches on.

• The display stays black or keeps resetting.

• The motor suddenly cuts out under load (bridge, hill).

Possible causes:

• A damaged battery pack (a fall, water, age).

• Contact problems in the battery holder, connector or cables.

• A fault in the BMS (the protection switches the battery off).

• Sometimes: a faulty motor or controller.

Important: do not keep trying endlessly. A damaged or overheated battery in particular can be a safety risk. Have the system and the battery checked by a specialist.

3. Error codes on the display of a mid-drive e-bike

Every manufacturer has its own error codes (Bosch, Bafang, Shimano, Yamaha and so on). Typical situations:

• Error messages that point to overheating or a mismatch in the battery voltage.

• Errors that come back after a reset or software update.

• Unexplained faults in wet or damp weather.

There are two kinds of problem here:

• Motor and sensor problems: often a job for the bike mechanic.

• Battery and BMS problems: this is where KWS Seuren comes in.

We test the battery off the bike for:

• voltage and capacity;

• behaviour under load;

• heat build-up;

• internal resistance and balance between the cells.

That shows whether the fault is in the battery or elsewhere in the system.

4. Battery no longer charges (properly)

Complaints:

• The charger stays on “green” and the battery does not seem to charge.

• The charger flashes red or keeps cutting out.

• The battery gets abnormally warm while charging.

Reasons:

• A faulty charger (always have this checked first).

• A damaged charging port or cable.

• Internal protection in the battery that blocks further charging.

• Deep discharge: the battery has been run down too far.

The same applies here: do not experiment yourself with “tricks” from the internet. Unsafe charging is a major fire risk. Have the battery and charger checked together in a professional test set-up.