Is the Hub Motor Really "Weak"?

November 14, 2023

Who doesn't enjoy the feeling of effortlessly surpassing others? Nowadays, an increasing number of new electric-assist bicycles are solidifying their presence in the market, with significant differences in functionality, performance, and price. One noticeable distinction lies in the choice between mid-drive motors and hub motors. Today, we sit down with motor experts to explore the differences between these two motor types.

From high-performance eMTBs to stylish urban bicycles, and from regular road bikes to gravel bikes, electric-assist systems have been adapted to various models. Currently, there are two main types of drive systems on the market: mid-drive motors and hub motors. These motors differ not only in their installation location but also in their functional effects.

Hub motors, especially, are not well-understood by many, often considered as the "little brother" to mid-drive motors, with a perception of lagging behind in development. However, they do possess notable advantages and performance. In this discussion, we invited motor experts from Germany's Mahle company to break down stereotypes and misconceptions about these two motor systems. Mahle is considered a "technology expert" in the automotive industry, but they have also been involved in the electric-assist bicycle market for years, collaborating with top bicycle brands.

For instance, Mahle collaborated with Specialized to develop the SL 1.1 mid-drive motor, helping the S-Works Turbo Creo SL win the 2019 electric-assist road bike evaluation.

In the realm of hub motors, Mahle is at the forefront, providing compact X20 motor drive systems for major brands like SCOTT, Mondraker, and BMC.

Many people may think that comparing mid-drive motors and hub motors is like comparing apples and oranges—simply a matter of budget or preference. However, for cyclists looking to purchase an electric-assist bicycle, having a deeper understanding of the technical aspects is beneficial, and expert insights can provide valuable clarity.

Not All Hub Motors Are the Same 

It's not only challenging to compare hub motors and mid-drive motors, but there are also differences among various hub motors. Even within the same type of hub motor, there can be subcategories. Just as mid-drive motors have light assist and full assist power units, hub motors also have different drive mechanisms, with their design concepts differing significantly.

Distinguishing Gear Hub Motors and Direct-Drive Hub Motors 

In general, direct-drive hub motors tend to be larger and heavier. They don't rely on internal gearboxes or flywheels but directly apply the transmitted force to the wheel. This type of hub motor is primarily used in niche cargo electric-assist bicycle models, and thus, we won't delve into it further. Instead, let's focus on geared hub motors.

Geared hub motors are the standard solution for lightweight electric-assist road bikes, gravel bikes, and urban bicycles. These motors are typically smaller, lighter, and equipped with an internal gearbox. As the motor rotates the central gear at high speed, it can be converted into slower rotational speeds through planetary gears to match the reasonable speed of the rear wheel. This method helps the motor operate more efficiently and at a faster speed. In theory, hub motors have design advantages, but in actual riding, numerous external factors can influence the hub motor's operation and performance efficiency, leading to misconceptions and rumors about hub motors that need to be addressed.

Misconception 1: Hub Motors are Technologically Inferior to Mid-Drive Motors 

In some stereotypes, mid-drive motors have long been synonymous with high technology. Early on, when entering a bicycle shop, the first electric-assist bicycles seen were often equipped with lower-cost hub motors, lacking the flashy new technologies.

However, in terms of technology, modern hub motors are not necessarily inferior to mid-drive motors. If paired with high-tech systems and auxiliary devices commonly used in mid-drive motor systems, hub motors can provide an excellent riding experience.

With advancements in hub motor technology, many products now feature sensors such as torque and cadence sensors, speed and acceleration sensors, tilt sensors, and more, offering data comparable to mid-drive motors. Additionally, cutting-edge technologies like independently adjustable motor characteristics, connectivity features, modular battery designs, etc., can be found in current hub motor electric-assist bicycles.

It can be confidently stated that the significant gap in technology between mid-drive motors and hub motors is narrowing, signaling the end of an era. The misconception that hub motors are technologically inferior to mid-drive motors needs to be erased from our minds.

Misconception 2: Hub Motors are Suitable for Low-cost Electric-assist Bicycles 

This perspective is overly simplistic. Whether it's hub motors or mid-drive motors, there are products catering to low, mid, and high-end markets. However, the prevailing view is that hub motors are typically used in budget electric-assist bicycles, while high-end electric-assist bicycles invariably use mid-drive motors.

The market trend is currently undergoing a transformation, presenting a completely different landscape from before in the electric-assist bicycle market. Currently, electric-assist bicycles are still priced quite high, and at such elevated prices, manufacturers have enough budget to purchase any motor system to install on their bicycles.

Undoubtedly, the electric-assist bicycle market is flooded with numerous low-cost hub motors, reducing the entry barrier for purchasing electric-assist bicycles. However, for manufacturers targeting the high-end market segment, the impact of motor system prices on the overall bike price is not as decisive as one might think.

Manufacturers choosing hub motors for a high-end electric-assist bicycle do so because they recognize the highly integrated advantages of hub motors, ensuring excellent performance, and not just to save costs.

Misconception 3: Electric-assist Bicycles with Hub Motors Have Unbalanced Weight Distribution 

Hub motors and mid-drive motors have different weight distributions, an undeniable fact. For electric-assist bicycles, mid-drive motors are installed between the wheels with a lower center of gravity, usually having a beneficial impact. When a hub motor is installed, most of the weight shifts to the rear wheel. However, only riders sensitive to weight distribution differences may notice the distinction.

Mahle's X20 motor is one of the lightest hub motors on the market, weighing only 1.4 kilograms. In our testing, we observed a slightly stronger drag on the rear wheel on inclines. For instance, on the Mondraker Dusty XR gravel e-bike, the additional weight added to the rear of the bike caused the rear wheel to feel bumpy on rough descents.

However, if you're not an avid downhill enthusiast and don't require an extremely agile bike, an excellent electric-assist road bike with a hub motor can still provide an enjoyable riding experience.

Overall, the unique weight distribution of hub motors has only a minor impact on the overall bike riding experience. Importantly, weight distribution needs to harmonize with the frame's geometry, putting manufacturers to the ultimate test.

Currently, manufacturers using hub motor systems for electric-assist bicycles have a high degree of design freedom in frame design, geometry, overall weight, etc. In actual riding tests, riders can quickly adapt to the weight distribution of hub motor systems.

Nevertheless, hub motors don't offer a uniform riding feel. This primarily depends on how electric-assist bicycle manufacturers define their products. Whether dynamic and lively, leisurely and slow, different electric-assist bicycles with different hub motors can provide different riding experiences, even giving rise to the existence of dual-drive electric-assist bicycles like the FMoser Road Force.

This versatile electric-assist road bike features two rear wheels, one with a hub motor and one without. FMoser even won a design innovation award for this trend-setting concept.

Misconception 4: Hub Motors Are Weaker? Are Mid-Drive Motors Stronger? 

Due to differences in weight and appearance, hub motors are often considered "weak" in terms of power, while robust mid-drive motors are synonymous with strength. Currently, intuitive torque and weight data have become key points of promotion for many motor manufacturers. However, these factors themselves are not decisive for the performance impact on motor systems.

Since hub motors directly apply force to the wheel without the losses generated by a transmission system, even if the on-paper data appears poor, it doesn't necessarily mean the actual output of hub motors is "weak." Mahle's experts believe that an excellent motor system isn't solely determined by on-paper data; it requires tuning the appropriate torque range based on actual riding conditions, rather than blindly pursuing maximum power output.

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