Test / E-Bike Drive: With the M40, automotive supplier Mahle is breaking new ground and presenting its first full-power mid-drive motor. The key specifications of the Mahle M40 read like a wish list for many e-bikers: 105 Newton meters of torque, up to 850 watts of peak power, and all this with a motor weight of just 2,5 kilograms. We had the opportunity to test the system extensively in the lab and on the trail and determine whether the drive system delivers on its promises in practice.
It's remarkable how many new drive system manufacturers and mid-drive motors are currently entering the market. While some names might require a second look, Mahle is already a well-known name in the bicycle industry. The automotive supplier has made a name for itself in recent years, primarily through its hub motors like the X20 and X35, which have become almost standard in the e-road and e-gravel sectors. However, what many don't know is that Mahle has been manufacturing mid-drive motors for some time, including the Specialized SL 1.1 and 1.2 drives for the popular Levo SL models. With the new M40, the manufacturer is now combining all its experience into a dedicated system for bicycle manufacturers.
Mahle M40 Technical Data: An impressive power-to-weight ratio
The Mahle M40 is undoubtedly one of the most exciting motors introduced recently. On paper, its specifications are truly impressive. A maximum torque of 105 Nm and a peak output of 850 watts are remarkable in this weight class. For comparison, a Bosch Performance Line CX (Gen 5) weighs more and nominally offers less torque. Mahle thus achieves a power-to-weight ratio that comes very close to the much-discussed DJI Avinox and puts established market leaders under pressure.
This performance is made possible, among other things, by the system's 48-volt architecture. Compared to the more common 36-volt systems, this higher voltage ensures greater efficiency and improved thermal performance, as less current is required for the same power output. This allows the engineers to build a compact and lightweight motor despite its high performance. The magnesium housing reduces the weight to the aforementioned 2,5 kilograms.
Integration and design
A look at the motor within the frame reveals its extremely compact design. The M40 is bolted to the frame at three points. Mahle expects this to result in a better distribution of the connection forces. The shape is also striking: the motor tapers sharply towards the rear. This creates valuable space in the bottom bracket area for the rear suspension kinematics. Bicycle manufacturers thus gain more freedom in designing the suspension systems and don't necessarily have to build the frame "around the motor."
The ecosystem: batteries, displays, and remotes
A motor alone does not make an e-bike. Mahle offers a complete system for the M40 that can be modularly adapted to the needs of bicycle manufacturers.
The energy storage units: iM5 and iM8
Two internal batteries are available at launch, both manufactured in Europe and boasting impressive energy density:
- iM5: With a capacity of 534 watt-hours, this battery is designed for lightweight e-MTBs. According to the manufacturer, it weighs approximately 2,5 kilograms.
- iM8: For long-distance travel, there's the 800-watt-hour version, which has the same form factor (cross-section) but is longer. Its weight of 3,8 kg is also impressive.
Mahle is planning a range extender, which should be available in the future to further increase the range. However, no data or exact date is yet available.
The charger is a slight disappointment: with "only" a 4A charging current, it can't compete with the fast chargers from DJI or Specialized. However, since the system operates at 48V and the final charging voltage is 54V, the charger still offers a charging power of over 200W and is therefore significantly more powerful than, for example, a 4A charger from Bosch with 36V.
operating units
Mahle's controls take a minimalist approach with a sporty focus. The display, called "Head Unit+", is integrated into the top tube. It features a 1,9-inch color screen and displays the most important riding data. While its slightly wider bezels don't give it quite the same futuristic look as solutions from TQ or DJI, it serves its purpose and is easy to read. One drawback for touring cyclists: there's no USB-C port on the display for charging a smartphone.
Two options are available for operation via the handlebars:
- Duo Remote: Known from hub motors, wired, two buttons.
- Trio Remote: New for the M40, wireless, three buttons.
The Trio Remote was particularly impressive in our initial hands-on, as the third button significantly simplifies menu navigation and screen switching. The buttons offer good tactile feedback and can even be used with gloves.
Laboratory results: The M40 on the test bench
Before hitting the trail, the M40 had to reveal its true performance on the test bench. The results largely confirmed the manufacturer's specifications, but also revealed some interesting characteristics in the tuning.
Maximum performance and efficiency
In our tests, the motor reached a peak output of around 800 watts. This is just under 50 watts below the manufacturer's specification, but in practice, it's an excellent value, making it one of the most powerful motors we've ever measured. It's important to note that the motor delivers this peak output primarily at higher cadences of around 90 to 95 revolutions per minute. In our standardized "high-performance test" at 250 W input power and a cadence of around 75 rpm, the M40, with just over 700 watts, ranks third behind the DJI Avinox and the TQ HPR120s.
Power delivery and support curve
The comparison of the support levels is particularly interesting. Mahle offers three modes as standard: L1 (Eco), L2 (Trail), and L3 (Turbo/Boost). The measurement curves show a linear behavior. Unlike, for example, Bosch's eMTB mode, which reacts progressively to rider input (low rider effort = low support, high rider effort = disproportionately high support), the curve for the Mahle M40 rises steadily.
The most powerful mode requires significant effort from the rider to unleash the full power. This provides a very natural riding feel, but with plenty of power at your disposal. For those who prefer more instant acceleration, the software allows manufacturers and end users extensive customization. The assistance can be increased to up to 600% (relative to the rider's effort), which should drastically alter the motor's character. Riders can adjust these settings either via the corresponding smartphone app or directly on the bike itself.
Thermal stability (Derating)
A critical factor with compact, high-performance motors is often heat generation. This is where the 48-volt system demonstrates its advantages. In our 15-minute load test under full load, the M40 showed no significant drop in performance. Only after approximately 20 minutes of continuous load did the derating gently intervene, gradually reducing the power output, not abruptly. The housing temperature stabilized at around 80 degrees Celsius – warm, but safe. This means the small Mahle motor even outperforms significantly larger units like the Bosch CX Gen 5 in terms of thermal performance.
The practical test: How the Mahle M40 drives
Enough of the theory. How does this powerhouse feel on the trail? To put it simply: The M40 is incredibly fun and offers plenty of power and punch, yet still provides fine modulation and a natural riding feel.
Driving feel and modulation
The bike's responsiveness is noticeable from the very first meters. The motor responds extremely directly to the pedals without feeling twitchy. In the second assistance level (L2), the bike can be expertly maneuvered through technical sections. The power delivery feels organic; you never feel like a passenger on your own bike. The "moped feeling," where you just let go of the pedals and the motor does the rest, doesn't occur here – and that's meant as a compliment.
The power modulation is excellent. Mahle doesn't use a classic spoke magnet, but rather a perforated disc with 42 holes at the brake disc mount, which is scanned by two sensors. This results in 84 data points per wheel revolution. The system therefore knows extremely precisely what the rear wheel is doing. Even on slippery surfaces or steep climbs, traction can be finely controlled.
Intelligent features: Gear detection and hill brake
A highlight of the software is the gear recognition. The system registers – even with mechanical shifting systems – which sprocket the chain is currently on. Mahle uses this information to intelligently control the torque. The full 105 Nm, for example, is primarily available in the higher gears, where it is needed to improve modulation in the lower gears.
Another feature that has proven useful in practice is the "Hill Brake" (hill start assist). If you have to dismount on steep terrain, the motor prevents the bike from rolling backward when you press the pedals. It works intuitively: one foot on the pedal is all it takes, and the system locks the drive, much like a handbrake. To continue riding, you simply press the pedals again.
Dynamic Overrun
In the latest software version, Mahle has also improved the "power boost" feature. The so-called "Motor Dynamic Overrun" now behaves very similarly to Bosch's Extended Boost. A quick kick of the pedals before an obstacle is all it takes, and the motor propels the bike smoothly over the step without requiring any further pedaling. The length of the boost (up to two meters) correlates with the intensity of the pedal kick. In technical uphill sections, this is a powerful tool that has been implemented precisely, although not quite as responsively as the Bosch system.
Noise level: Not completely silent
Where there's light, there's usually some shadow. In the case of the Mahle M40, this concerns the acoustics. The motor is audible uphill. It's louder than a Bosch CX Gen 5 or DJI Avinox and more on par with a Shimano EP801 or Bosch CX Gen 4. It's not an unpleasant noise, but certainly noticeable for those who prefer a silent ride.
The assessment becomes more complex on downhill sections. During the test rides, a certain rattling noise was noticeable coming from the motor area. It's currently difficult to say definitively whether this is the classic freewheel rattle familiar from Shimano or Bosch systems, or whether it's due to the integration of the cables and battery into the pre-production frame. The stationary "shake test" was largely unremarkable, which gives hope that production bikes will run more smoothly. Regarding this issue, we'll unfortunately have to wait for more extensive experience.
Availability
The biggest hurdle for potential buyers is currently availability. At launch, the M40 is primarily being used by niche manufacturers and direct-to-consumer brands (such as Labyrinth and Kristall). Many of these bikes utilize an "Open Mold" carbon frame co-developed by Mahle, which offers excellent geometry. It remains to be seen when the major mainstream manufacturers will jump on the bandwagon.
Conclusion: Mahle M40
With the M40, Mahle has made an impressive entry into the full-power mid-drive motor segment. Its power-to-weight ratio is currently virtually unrivaled, especially when considering its robustness and thermal performance. The motor offers a fantastic, natural riding feel that rewards sporty riders and, thanks to features like precise overrun, also excels in technical terrain.
The system isn't perfect – the display looks a bit dated and the noise level is noticeable – but the overall package is compelling. For e-mountain bikers looking for a lightweight bike but not wanting to sacrifice full torque, the Mahle M40 is one of the most exciting options of the year. Now it's up to bicycle manufacturers to translate this potential into attractive production bikes.