RH205 motor windings
07/10/2026From the 250W e-bike to the powerful rear motor kit
07/10/2026
Crank drive motor: the rich man’s alternative?
The Chinese mass
China being the great supplier of electric motors for bikes, the most commonly used motors originate there.
The Chinese need reliable motors, with variable power (from small folding bikes to delivery tricycles) and inexpensive. Besides the domestic market, China also supplies Europe and the United States. With a motor production counted in tens of millions each year, economies of scale are very significant and the price of these motors is hyper competitive: initially intended for the local market, once exported the price looks derisory by Western standards.
In Europe, Europeanised 8FUN Bafang type motors (<250W) are very present in integrated products or kits. In North America it is rather Nine Continent that is king of the market thanks to its price, its reliability and its ability to handle high power.
In all cases these are hub motors, motors integrated in the wheel, allowing simple installation on almost all types of bikes, even specific bikes such as small folding bikes, recumbents, trikes, cargo bikes…
The Western alternative: the crank drive motor
These millions of motors distributed from China do not prevent some manufacturers from redefining the concept of the electric bike motor: indeed, brands such as Bosch or Panasonic offer “crank drive motors”. These are motors that are not integrated into the wheel hub, but take a central position on the bike, very close to the crank axle.
Below is a diagram of a crank drive motor from the Kalkhoff brand (visible on this page) which uses the Panasonic block:
Ci-dessous a diagram from the Kalkhoff brand (visible on this page) showing the operating principle of the crank drive motor:
Below, a Scott with a Bosch crank drive motor taken from the Scott website:
The Bosch motor, for its part, directly drives the crank (details on the BOSCH site). This solution integrates the motor, transmission, sensors and electronic control!
It is a beautiful technological solution and BOSCH already equips some thirty bike brands, including Scott, Cannondale, Merida etc…
Logically, crank drive motors are installed on bikes whose frame is defined from the start to receive the block. They are therefore installed on specific and rather expensive bikes, whose overall specifications are pulled upwards. For a Kalkhoff bike, consider that the entry ticket is around €3,000.
For some this will seem consistent with their way of operating. For the person in the process of a first experience, it may seem far too high. For someone who already knows the electric bike and is able to integrate the various components themselves, such a budget provides the means to build a “dream” bike.
China too!
The Chinese are always quick to seize market opportunities. Since 2012 a crank drive motor manufacturer has offered inexpensive kits: GNGElectric. This kit has gone through several versions (at least the manufacturer listens to user feedback), notably because the drive belt was quickly destroyed by mechanical constraints.
In the case of this kit, the advantage is being able to keep (part of) your original transmission, at least the rear wheel and the gear system.
A sports bike?
The crank drive motor drives the cranks! Consequently, the motor uses the bike’s transmission (gears) and the sensor-determined assistance lets the cyclist pedal at a constant speed, whatever the route profile. For the person who wants to do sport and whose pedalling rate matches the motor speed, it is perfect.
Moreover, the motor position provides beautiful balance when you leave the road to attack cross-country paths.
Bikes more expensive than cars!
If you have between $6,000 and $13,000, you can buy the bikes offered by Optibike.
Below is the R11 at $13,900, quoted for 53km/h over 65 kilometres.
The crank drive motor is sometimes a piece of jewellery and the most expensive bikes use this solution: in the other case, the exorbitant price would seem totally unjustified for motors whose specifications and price are well known.
Below is the Audi “E-TRON” (apologies for the name) with crank drive motor… Splendid, but its future price is estimated at $20,000…
The advantages of the crank drive motor
- a beautiful piece of mechanics, technical refinement and sophistication of the whole, specific frame (excluding the GNG kit!) dedicated to the motor
- use of the transmission (gears) integrated in the bike, constant pedalling rate for the user whatever the terrain profile
- motor placed ideally from a centre-of-gravity point of view for off-road
The disadvantages
- high cost of the bike
- complex motor installed on a specific frame (you cannot keep the bike you were going to electrify)
- “tuning” impossible (in some cases the motor has a specific sprocket that can be changed and that lets you go longer)
- motor and controller intrinsically linked, changing to a more powerful or different controller is almost impossible
- “electric scooter” mode impossible, it is the torque sensor that triggers the assistance
- resale of the motor alone on the second-hand market impossible
- repairs by yourself almost impossible
- on the least expensive systems, reliability can be improved: chain or belt breakage
Conclusion
- an expensive (but effective) solution, intended for the Western cyclist with means
- a “all-in-one” monolithic and closed manufacturer solution, for the enthusiast who loves to define, design and improve
