An electric bike wouldn’t be an electric bike without its motor and battery.

There’s a range of different motor systems out there from different brands, and it can be confusing. 

At Rothar, we stock Shimano, Bosch and Mahle, and we are an approved dealer for those three brands, meaning we can diagnose your bike, update your system and get spares for your bike if needed.


The basics

Each motor tends to be selected for its performance characteristics and how well it fits with the intended use of each ebike model. Below are the two different types of systems we sell.

Mid-mounted motors

Mid-mounted motors sit in the area where the bottom bracket is usually found.

Mid-mounted motors are found across all different types of electric bikes. They work particularly well for electric mountain bikes because the weight is central and low down

Rear-hub motors

Rear-hub motors are usually found on hybrids and some of the best electric road bikes.

Rear-hub motors look very sleek and, at first glance, it’s often hard to tell the bike they’re fitted to is an electric bike.

Battery placement

Batteries, meanwhile, might be mounted on top of the down tube or along the front of the seat tube.

Internal batteries housed in the down tube that are either removable or fixed in place are also a popular option, particularly on mountain bikes.

Some city hybrids often have the battery mounted under the luggage rack.

A removable battery has the advantage that you can take it indoors to charge it, whereas you’ll need an electrical socket close to your bike to charge it otherwise. On the other hand, a non-removable battery may look neater, is better protected and less prone to theft.


Electric bike motor power and torque explained

Electric bike motor power output is normally measured in watts.

Electric bike laws in the European Union state a motor’s continuous power output has to be limited to 250 watts. The majority of motors can put out over the 250 watts maximum power allowed, providing considerably higher peak power over short time periods.

A motor’s maximum torque is the more important performance figure. The peak torque a motor is able to deliver also varies more between motor systems.

Denoted in Newton metres, or Nm, this measures how much turning force the motor gives out.

On an electric mountain bike, you’ll find situations where it’s important to have plenty of torque on hand to help you quickly get over obstacles and up steep gradients.

The best electric mountain bikes typically come with higher-spec motor systems with higher torque output, and the same is true of electric cargo bikes.

Electric gravel bikes or road bikes may not require as much oomph, or a manufacturer may choose to spec a less powerful motor to provide a more natural ride feel.

Assistance levels and displays

Electric bike motor systems typically come with a separate controller so you can set the assistance level you want. There are usually between three and five assistance levels, offering an increasing amount of power, as well as the option to pedal without assistance, useful if you’re trying to get fit on your electric bike.

As you’d expect, the less assistance you dial in, the longer the ebike’s battery will last. It’s a good idea to dial it up when you hit obstacles such as a hill or for stop/start riding, and drop it down again when the terrain is easier.

Some systems have an option called ‘boost’ or ‘turbo’ mode. This gives you extra power above 250 watts to help with quick starts or steep climbs.

The controller usually sits on the bike’s handlebar, although some are set into the top tube. Designs vary from those that give you a screen with loads of stats, sometimes including navigation, through to a minimalist single button and LEDs to show battery and assistance levels.

Most electric bike motor systems come with an app, which you can use to monitor their status and battery life.

Some allow you to change settings such as the amount of assistance you get at each level, and some use your smartphone as the controller for the ebike. Many apps give you navigation, ride stats and other data too.


Mid-drive motor systems

The key electric motor brands using mid-drive motor placement are Bosch and Shimano Steps.

Bosch electric bike motors explained

Bosch has six different variants of its mid-drive motor unit, with some having hub gear and derailleur gear variants.

All offer four levels of assistance, with the maximum torque on offer ranging from 40Nm for the Active Line units up to 85Nm for the Performance Line CX. Motor weights are between 2.9kg and 3.2kg.

You’re more likely to see the Performance Line CX motors on electric mountain bikes and electric gravel bikes, which demand plenty of torque. Bosch Active Line motors are more commonly seen on electric hybrid bikes.


Bosch electric bike motor specs

 Motor weight Peak power Peak torque
Bosch Performance Line CX 2.9kg 250 watts 85Nm
Bosch Performance Line Speed 2.9kg 250 watts 85Nm
Bosch Performance Line 3.2kg 250 watts 75Nm
Bosch Cargo Line 2.9kg 250 watts 85Nm
Bosch Active Line Plus 3.2kg 250 watts 50Nm
Bosch Active Line 2.9kg 250 watts 40Nm

Bosch electric bike battery options

  • Battery capacity: 300-725Wh
  • Battery weight: 2.5-4.0kg

Bosch electric bike battery options

  • Battery capacity: 300-725Wh
  • Battery weight: 2.5-4.0kg

Orbea Katu with a Bosch Active Line motor, perfect for the city



Shimano Steps electric bike motors explained

Shimano has targeted its Steps motor system at urban and eMTB riders, although it’s now expanding its support to e-road and e-gravel bikes too, offering integration with its Di2 electronic groupset shifters.

There are five motors available. The mountain bike-oriented E7000 and latest EP6 and EP8 models come with 60Nm or 85Nm torque and a large-capacity battery of up to 630Wh. This can be mounted either externally on the down tube or within the frame.

The EP801 motor (more commonly known as EP8) replaced Shimano’s original EP8000 motor. This matches the 85Nm torque output of Bosch’s highest-output Performance Line CX, while dropping the weight from the other MTB-oriented Steps motors.

Shimano says the new EP6 motor provides the output of the EP8 in a more affordable package. It’s slightly heavier though. Both the EP6 and EP8 motors offer features such as automatic shifting when paired with an electronic groupset, and a system to allow shifting without needing to pedal.

Meanwhile, the E6100 motor is aimed at hybrid ebikes, the EP8 Cargo, EP6 Cargo and E6100 Cargo are – as the name suggests – designed for use on cargo bikes. These give higher torque from lower speeds compared to the standard units.


Shimano Steps motors specs

 Motor weight Peak power Peak torque
Shimano Steps EP8 (EP801) 2.7kg 250 watts 85Nm
Shimano Steps EP6 (EP600) 3.0kg 250 watts 85Nm
Shimano Steps E7000 2.8kg 250 watts 60Nm
Shimano Steps E6100 2.8kg 250 watts 60Nm
Shimano Steps E5000 2.4kg 250 watts



Shimano Steps battery specs

  • Battery capacity: 418-630Wh
  • Battery weight: 2.6-3kg


The magnificent Achielle Annette electric bike, sporting a Shimano steps system


Rear-hub motor systems

Positioning a motor in the rear hub works well on road and hybrid ebikes, where there’s not as much need to shift your weight around compared to riding an eMTB.

Because much of the rider’s weight sits over the rear wheel, there’s plenty of traction. Since the motor’s power isn’t going through the drivetrain, there’s also no extra wear and no need to beef it up to deal with the motor’s torque.


Mahle ebikemotion motors explained

The Mahle ebikemotion system has a rear-hub motor, powered by an internal battery in the down tube.

Mahle now has two ebikemotion rear-hub motors – the original X35 and the newer, more compact X20.

The original X35 motor has 40Nm power output, while the new X20 ups that to 55Nm. Both systems have batteries of around 250Wh, while the X20 also has a 350Wh option.

Its compact size makes for a bike profile that’s not that different from a regular pedal-powered bike. There’s the option to add a bottle cage battery to double the range.

The iWoc controller options from the brand include a low-profile button mounted on the top tube, as well as bar-mounted units. There’s BLE and ANT+ connectivity and an app that enables you to tune the motor, and has an option to control output based on your heart rate.

The gorgeous Orbea Gain D30 IX, powered by a Mahle hub motor, to get you up those hills without spoiling the fun


Mahle ebikemotion specs

Motor weight Peak power Torque Battery capacity Battery weight
Mahle ebikemotion X20 1.4kg 250W 55Nm 250Wh/350Wh 1.8kg
Mahle ebikemotion X35 1.5kg 250 watts 40Nm 250Wh 2.0kg