Buying advice for e-bike motors: A comparison of the advantages and disadvantages of the different motor types
Georg Bleicher
· 07.09.2024
Many of us have almost got used to the fact that the motor is located in the bottom bracket area. On the one hand, this is due to the fact that this mid-motor is by far the most commonly installed in its many variants, but on the other hand, the other two variants, i.e. front and rear hub motors, are often overlooked. Depending on the model, they can be as small as a gear hub (rear) or a slightly larger hub dynamo. So a mid-motor is not everything, even if some people think it is.
Why does it matter where the motor is located? On a 25-kilo e-bike, the drive system consisting of the motor, battery, controller and controls can easily weigh around seven to eight kilograms, which is almost a third. The weight distribution is therefore absolutely relevant for handling when riding, but also when manoeuvring and pushing, as we will see in a moment. Apart from this, the different engines also have different characteristics in terms of power delivery and other factors.
Front motor: pulling instead of pushing
Actually a good idea: the drive in the front wheel. Simple installation - even retrofitting is easy with some manufacturers using a ready-to-use replacement front wheel with motor - low effort, low costs. This was another reason why the front-wheel drive was hugely successful at the beginning of the e-bike era. However, some negative influences soon became apparent: the force with which the front wheel pulls puts considerable strain on the fork and the front frame - incidentally one of the reasons why we would also advise against retrofitting simple bikes with a front motor. Both are not designed to withstand this force and may well suffer safety-relevant damage. Increased tyre slip can also be a problem on a new bike already equipped with a front motor. Particularly on inclines and loose surfaces, abrupt pedalling can quickly cause the front wheel to spin. However, in recent years, sophisticated sensor technology and ever-improving control have ensured that the front wheel does not act too independently.
However, front hub drives can still be useful for (especially heavy) cargo bikes. Due to the weight on the axle, the motor acts less abruptly. For example, there are still cargo bikes that are successfully supported by a hub motor in the front wheel, such as the Musketier business cargo bike with an Ezee motor in the front wheel. Rehab tricycles are also often equipped with the inexpensive and easy to realise front-wheel drive (see www.radkutsche.de/musketier).
Front engine: advantages and disadvantages
+ favourable
+ Can be realised very quietly
+ Technically easy to implement
+ All circuit variants can be combined
+ Relatively light
- disturbing influences on the steering (sluggish) and possibly on the suspension
- early slipping with low axle load, also on asphalt or in wet conditions on hills
- High load on fork and head tube
- Usually complicated removal of the front wheel
> Useful areas of applicationCargo bikes with a lot of weight on the front wheel (Long John, heavy-duty bikes, rehab tricycles), entry-level e-bikes.
Rear engine: built-in tailwind
Almost as easy to design as the front motor, the hub drive for the rear wheel quickly became something of a standard in the early years of e-bikes. There were geared motors and direct drives very early on: with its current version of the Neodrive Z20, Alber is still one of the most important representatives of the rear motor today. This is a so-called direct drive, i.e. a hub motor without a gearbox. Its advantages: It is perhaps the quietest motor on the market, and it can recuperate as a direct motor.
This means that it recharges the battery when travelling downhill. The recuperation is definitely in the significant range - around ten per cent can be recovered when you are driving on hilly terrain. The recuperation - which can be selected - then simultaneously acts like an engine brake on the car, meaning you wear out your brakes less. The automotive supplier Mahle has classic representatives of a geared rear engine in its programme. However, the main advantage over the mid-engine is that the wear on the chain, sprocket and pinion is only as high or even lower than on the biobike, as the power of the motor is applied directly to the rear wheel and not to the chainring.
Advantages and disadvantages of the rear engine
+ Recuperation possible (direct drive only).
+ uncomplicated installation
+ Inconspicuous size (gear motor only)
+ Quiet to silent (direct drive)
- usually less harmonious pedalling than with the mid-motor (often missing torque sensor).
- No hub gears possible
- Often poorer performance on the mountain
- Some variants have a tendency to overheat on long inclines
> Useful area of application: Cargo bikes, city bikes, commuter bikes, each without rear suspension
Smartness is sexy
The AI trend does not stop at e-bikes, on the contrary: Bosch calls its new generation the Smart System. What's so clever about these motors? At Bosch, these include special support modes such as Tour +. This eliminates the need for manual switching on longer journeys and regulates the assistance itself as required.
Smart, you can also switch to automatic mode with Pinions MGU which will also be available in software in the Pinions that are already active from the summer. The system selects the right gear for the speed and driving situation.
Mid-mounted engines: Power comes from the centre
For us, this is already a classic and at the same time the variant with the most convincing performance: the mid-motor. Its big advantage: thanks to the simple integration of a torque sensor, this type of motor is very good at creating a harmonious pedalling feel - some Shimano, Bosch or even the new Bafang motors and many others demonstrate this. Its second advantage: a good centre of gravity low in the middle of the bike - another reason why the motor has become the favourite of E-MTB riders. After all, if you're going to add weight, then put it in the centre!
Today, these engines can boast the most powerful thrust. The Bosch Performance Line CX MTB motor delivers 85 Newton metres. and the SyncDrive (Giant) with 85 Newton metres, 95 even the Panasonic-GX Ultimate. Delta Electronics, an international company, has also just launched a mid-motor with 90 Nm. And the power would probably increase significantly if the chain, cogwheel and sprocket didn't have to transmit this force in a different way to the rear-mounted motor and were not subjected to so much stress.
It is true that some manufacturers offer shift detection, which means that the motors recognise the reduced pressure on the pedals for shifting and then reduce their force so that the next gear can be engaged more gently. Nevertheless, you can imagine that the chain, chainring and sprocket have a negative effect when a force of 800 watts is applied, which can easily be achieved with standard motors and strong legs - you can often hear this clearly.
Of course, energy is also lost in the process: in certain situations, a 45 Newton metre rear motor can deliver just as much thrust to the rear wheel as a mid-motor with 85, but the advantages outweigh the disadvantages in the eyes of the vast majority of e-bikers. The market power of mid-mounted motors is probably also the reason why these motors are developed in such fine detail and often have an almost impracticable number of customisable options such as anti-theft protection, navigation, freely selectable support modes and others. But this is also a software thing.
Advantages and disadvantages of the mid-motor
+ Very harmonious, natural pedalling
+ All shifting systems possible on the rear wheel
+ Central, low centre of gravity on the bike when the battery is placed on or in the down tube
+ Natural look (minimal assist motors)
- No recuperation
- High load on the mechanical drive (chain, sprocket, pinion) due to the total force applied (less with combined gear/motor systems)
- usually not very quiet
- usually larger Q-factor (distance between the two cranks) than a normal bottom bracket (e.g. 177 MM for Shimano EP801)
Special form: Motor-gear unit (MGU)
If you're ambitious and have developed a fantastic, encapsulated gearbox around the bottom bracket, it makes sense to integrate it into a motor, doesn't it? This is exactly what was expected of the creators of the Pinion gearbox, who then introduced the MGU (motor-gearbox unit) in 2023. The gearbox can now also shift automatically with a choice of nine or twelve gears and is perhaps something of a benchmark in the mid-engine sector. However, there are a few other manufacturers - major supplier Decathlon has presented its own gearbox-motor unit without gear steps together with E2Drives, and Brose also showed a concept study at Eurobike 2023, which is probably just about to be ready for use.
This is an exciting development that could perhaps lead us away from gear hubs or derailleur gears in the rear wheel in some areas of e-biking. In any case, industry experts expect that we are heading towards comfortable e-biking with little wear and tear and many automatic processes.
Minimal assist motors: the invisible force
Still a niche product in its early years, the minimal-assist motor has become increasingly popular - a sign of the dynamic diversification of the e-bike. The idea behind it is a sporty one, at least initially: The guys at Fazua, for example, wanted to build the smallest, lightest possible drive system that would ensure that even bikes where weight is very important don't have to do without an electric drive - and feel "organic". Mountain, fitness and gravel bikes or racing bikes are particularly suitable for this.
But now also typical commuter bikes. Here too, the winding in the motor and the software play a decisive role when it comes to the efficiency of the drive. These motors, especially the Fazua models, are designed to deliver a high yield at higher pedalling frequencies. Overall, this is somewhat less (with Fazua around 60 Newton metres of torque and a maximum of 450 watts) than with a drive trimmed for high performance, such as the Performance CX from Bosch.
The behaviour of the Fazua is similar to that of the TQ-HPR50 drive: 50 Newton metres released in perfect harmony with the pedal stroke. Minimal assists are generally combined with smaller batteries, simply because it is also about saving weight. For example, batteries with a capacity of 250-400 watt hours usually work with the small batteries, which can mean a range (with continuous use) of around 45 to 65 kilometres. In a similar vein the new "small" Bosch CX (55 Nm, 600 watts). It is designed for higher engine speeds and thus provides very efficient and harmonious support in light, sporty bikes.
TQ, Fazua and Bosch are roughly on a par with a motor weight of 1.9 to 2 kilos, and all offer a 400 or 450 Wh battery as standard. Visually, the TQ probably blends in best with the bike's appearance among the mid-drive motors. It is no coincidence that we are also experiencing a renaissance of the rear motor with integrated gearbox: It can be built easily and "invisibly" without much effort, and the sensor technology coupled with rear motors is now so sensitive that even those in need of harmony do not necessarily want to resort to mid-drive motors. The Mivice drive is a good example of this. For MTBs, however, the small mid-motor is the measure of all things due to the central centre of gravity.
Serial hybrids: The future is rolling in!
So far, you can't buy bikes with them in the private e-bike sector, but the serial hybrid is definitely on the rise. This does not mean a new motor, but a drive system: the motor can be a front or rear hub drive. However, it is controlled in a completely different way than usual: instead of using a chain or belt drive, you pedal into a generator to produce electricity. This electricity - supported by additional power from a battery - is fed directly to the motor and converted into motion. So far, serial hybrids (strictly speaking, our classic pedelec is a parallel hybrid, as the muscle power plus the motor provide the thrust) have almost only been found in commercial cargo bikes.
This technology still has two disadvantages: Power consumption is significantly higher than with the systems we are used to, and the feeling of pedalling and getting clear feedback from the chain or belt drive is not yet possible to a great extent with the serial hybrid. You sometimes "step into the void" or suddenly have more resistance on the same surface. But the software and hardware is getting better and better here too - this problem of "natural pedalling" will probably soon be solved.
But what are the advantages? No chain to get dirty, for example. There is also no need for a gearbox. But the most important thing is a practically maintenance-free and wear-free drive. Where there are no mechanics, they can't break. This saves trouble, time and money. The system is currently of particular interest to the transport sector - where the pedalling feel is less important than freedom from maintenance and robustness. Incidentally, e-bikes with a serial hybrid have only been classed as bicycles since 2022: Prior to this, a direct mechanical connection between the drive and the rider was required, meaning that e-bikes with serial hybrid drives fell under the "vehicle" category - with all the associated disadvantages.
When will the serial drive take over among pedelecs? Mechanically powered bikes and e-bikes will almost certainly be around for a very long time to come, especially in the sports sector. However, a slow, gradual transition can certainly be expected over the next few decades. Examples of this are Podbike Frikar and Mocci SPV.
Interview with Claus Fleischer, CEO of Bosch eBike Systeme: "Non-connected bikes will be the exception in the future."
We asked Claus Fleischer, CEO of Bosch eBike Systeme, what the software in an e-drive can do in general and specifically at Bosch.
MYBIKE: In addition to the electronics and mechanics, the software in a drive system is fundamental. Why is that?
Claus Fleischer: The software in an e-bike drive system regulates the motor power, monitors the batteries and provides riding modes and functions.
The software is essential for safety and efficiency, but also for the riding experience and shifting behaviour of the e-bike by coordinating the overall performance and responsiveness of the system. It is also the basis for networked e-biking with functions such as navigation, fitness tracking, customisation of riding modes via the eBike Flow app or our digital anti-theft protection.
For example, how does the control software of the new SX motor differ from that of the Performance CX drive in terms of motor characteristics?
While the control software of the Performance Line CX was developed for dynamic output, the focus of the Performance Line SX was entirely on a natural riding experience. We therefore designed the software specifically to meet the requirements of a lightweight, compact drive unit - for maximum riding enjoyment with lightweight eBikes. The solution for this was a new type of software that always provides riders with maximum torque or maximum power exactly when it is needed.
The connectivity of drive systems is also playing an increasingly important role. Where do we stand today and what does it currently make possible?
With our solutions, we merge the physical and digital experience through the use of apps and cloud services to create a unique experience for eBikers. In doing so, we connect our hardware components with digital features. With the help of smart functions and over-the-air updates, e-bikers can constantly enhance their riding experience. This offers customers added value in terms of comfort, functionality, safety and customisation. Non-connected eBikes will be the exception in future.
And how can we imagine transport and everyday practice when we look to the future?
Overall, e-biking is becoming more individualised and personal. In recent years, we have introduced many products and features that make e-biking more comfortable and safer, such as electronic shifting with eShift or the Bosch e-bike ABS. Our aim is to integrate bicycles and e-bikes into a future V2X ecosystem (network of vehicles and objects with each other; editor's note). Vehicles connected in this way can help prevent accidents.
