If you’re comfortable riding a bicycle, you’re already set for a hub-drive e-bike. However, mid-drive e-bikes, especially the powerful ones capable of straining your chain, require a slightly different approach. Don’t worry, the techniques are straightforward.
Mid-Drive E-Bikes Explained Simply
This guide expands on concepts initially discussed in a previous article about e-bike motor types, specifically focusing on how to maximize the lifespan and performance of your mid-drive system. Many online discussions about mid-drive e-bikes often circle back to the principles of efficient riding and maintenance, hence this dedicated guide. For those interested in the DIY aspect, we also have a companion piece: “Building a Bulletproof Mid-Drive E-Bike.”
Mid-drive motors are prevalent in today’s e-bike market, particularly in the e-mountain bike (eMTB) sector. Why are they so popular? Unlike hub motors that apply power directly to the wheel hub, mid-drive motors integrate with your bike’s drivetrain. Hub motors operate independently of your bike’s gears; you could theoretically pedal a hub-drive e-bike without a chain and still receive motor assistance. However, when tackling steep inclines or navigating challenging terrain, combining human pedal power with motor assistance to the rear wheel becomes crucial for stability and control.
Hub motors, being single-speed in their motor output, struggle with hill climbing. The conventional solution for hub motors is to increase power output significantly – often into the 3-6kW range, approaching electric motorcycle territory. Mid-drive motors, conversely, channel power through the bike’s gears and chain, mimicking the way you pedal. This integration with the drivetrain is advantageous for the same reasons gears are beneficial for traditional cycling.
It’s important to note that this is a generalization. While hub drives can be less efficient on steep hills at lower speeds without gears, modern hub-drive e-bikes often feature multiple Pedal Assist System (PAS) levels, sometimes even more than typical mid-drive systems. Furthermore, some hub-drive systems incorporate multiple front chainrings, offering gearing advantages. Human power input on any e-bike, even a high-power one, should not be underestimated. A rider’s 100-300W contribution can significantly impact real-world performance. Conversely, mid-drive systems in lower gears, while offering ample torque, can quickly reach high cadences that limit usable speed. You might find yourself shifting up to gain speed even with substantial torque available. Hub drives, by separating electric power from human-powered gearing, offer flexibility in combining electric assist with optimal gear ratios for climbing. Geared hub motors, in particular, offer significant advantages often overlooked.
Only the most dedicated cyclists willingly climb hills on single-speed bikes. So, why would that be ideal for an electric motor? The answer is, it’s not. While a powerful hub motor can assist on hills, it’s not the most efficient or stress-free approach for the motor or its internal gears. If you’ve only experienced hub-drive e-bikes, the effortless hill-climbing capability of a mid-drive will be a revelation. Select the appropriate gear, and the mid-drive e-bike conquers inclines with ease. It ascends steadily, just like a regular bike in a lower gear, but with added power.
Indeed, traction is a crucial factor. Sufficient tire grip is necessary for any bike, especially on loose surfaces or steep climbs.
The performance advantage of mid-drives becomes even clearer when considering motor specifications. Mid-drive motors often boast significantly higher torque output compared to hub motors. Typical hub motors deliver 40-60Nm of torque, with some reaching up to 80Nm. Production mid-drives commonly start around 80Nm and go much higher. Aftermarket mid-drive motors can achieve a staggering 120-250Nm of torque.
Cyc X1 mid-drive motor powering a Guerrilla Gravity Smash e-bike, delivering 180Nm of torque to the drivetrain.
The Cyc X1 motor shown above, powering a Guerrilla Gravity Smash, generates 180Nm of torque at the drivetrain. Combined with a small front chainring and a wide-range rear cassette, this setup provides exceptional climbing ability, capable of tackling incredibly steep inclines.
Understanding Mid-Drive Power
To appreciate the torque output of a mid-drive in practical terms, let’s convert Newton Meters (Nm) to the more familiar unit of Watts (W):
- The 180Nm motor pictured above can peak at 3000 Watts.
- Bafang BBSHD and Bafang Ultra motors can reach 1750 Watts peak power (the BBSHD can sustain this peak output, making it exceptionally powerful).
- A 48V Bafang BBS02 typically produces around 1000 Watts.
- Standard street-legal e-bike motors in the EU are nominally rated at 250 Watts (though manufacturers often exceed this limit).
- A fit cyclist on a traditional bike can sustain around 300 Watts for short periods.
- Professional cyclists can briefly generate close to 1000 Watts, but only for very short bursts.
The Power Factor
Indeed, mid-drive e-bikes channel substantial power through the drivetrain. This power often exceeds the design limits of standard bicycle components. So, how do you manage such power without damaging or breaking parts?
Bafang BBSHD motor powering a 2WD titanium fat tire e-bike, running on a 52V battery.
The BBSHD motor pictured above, powering a 2WD fat tire e-bike, runs on a 52V battery, delivering a sustained output of approximately 1500W when used at full throttle.
Riding Techniques for Mid-Drive Longevity
Riding a powerful mid-drive e-bike correctly isn’t difficult, but it requires attention to technique. The goal is not only to prevent immediate damage but also to minimize premature wear. The fundamental principle is: Keep the motor spinning.
Maintaining Motor Spin
A core principle for all electric motors is that electrical energy is converted into rotational motion, which propels the bike forward. Resistance to this rotation, however, transforms electrical energy into heat. Powerful mid-drive motors can generate significant heat rapidly if they are prevented from spinning freely. Beyond heat, excessive resistance can lead to mechanical failures.
52V BBSHD mid-drive motor on a Big Fat Dummy e-bike, configured for overland and trail riding with a 36T front chainring for increased torque.
Lugging a powerful mid-drive motor, meaning operating it under high load at low speed, can generate immense torque that can damage your drivetrain. This can manifest as chain breakage, bent chainrings, or damaged cassette cogs. Even less extreme lugging can overheat and damage the nylon gears inside the motor, leading to motor failure and requiring costly repairs. To prevent this, proper riding technique is essential.
Downshift When Stopping
Always downshift before coming to a stop, just as you would on a regular bike. Alternatively, maintain a gear position in the middle of your cassette when anticipating stops. This ensures that when you accelerate from a standstill, the motor can spin up quickly and smoothly without excessive strain on the drivetrain. Starting in too high a gear from a stop puts significant stress on the cassette body and freehub pawls, potentially leading to premature wear or failure of the freehub mechanism.
Example of freehub body damage after 1000 miles of mid-drive e-bike use, emphasizing the importance of proper shifting.
Downshifting mitigates this stress and prolongs the life of these components. Remember, downshifting is a good practice even on non-electric bikes.
Sidebar: A gear cluster, also known as a cassette, comprises multiple cogs. Smaller cogs correspond to higher gears (for speed), while larger cogs are lower gears (for torque and easier pedaling). The cluster shown is a SunRace CSMX8 11-46T, indicating a range from an 11-tooth smallest cog to a 46-tooth largest cog.
Upshift to Increase Speed
When accelerating or wanting to go faster on a mid-drive e-bike, upshift through the gears, similar to driving a manual transmission car. Allow the motor to reach its optimal RPM range in each gear before shifting to a higher gear (smaller cog). It’s often beneficial to choose a gear slightly lower (larger cog) than you would on a non-electric bike for similar situations.
This advice to stay in a lower gear needs clarification. While it’s true that mid-drives can reach cadence limits faster than regular bikes or lower-powered hub drives, sticking to excessively low gears will severely limit your speed, especially uphill. Instead of crawling, aim to use 2-3 gears higher than you would typically use on a non-electric bike for climbing. The mid-drive system is designed to handle this. You don’t need to maximize power output constantly; often, 500W is sufficient. By using a slightly higher gear and modulating the Pedal Assist System (PAS) or throttle, you gain more control over speed and power delivery, especially when navigating obstacles. This allows for greater flexibility and efficiency compared to relying on very low gears and maximum motor output. The increased torque of a mid-drive fundamentally changes the optimal gear ratios compared to a traditional bicycle.
Your e-bike will reach similar top speeds in both high and slightly lower gears, but it will accelerate more quickly in the slightly lower gear due to the motor operating more efficiently. This principle of not lugging the motor applies here as well, encouraging you to let the mid-drive spin the drivetrain at a higher cadence than you might on a non-motorized bike. This isn’t about simply relying on the throttle for effortless riding. Instead, use the motor assist to enable a higher cadence than you could sustain under the same load without assistance.
Think of your mid-drive e-bike like a sports car with a manual gearbox. Between gear changes, briefly reduce power (stop pedaling or release the throttle), shift, and then re-apply power. If your e-bike has a gear sensor, this power interruption is often automated. If you prefer to pedal without using the throttle, select a comfortable low PAS level and maintain a fast pedal cadence using appropriate gear selection, just like on a regular bike. Avoid slow, forceful pedaling, especially uphill. Be a “spinner,” not a “masher.” On flat ground or downhill, less emphasis on cadence is needed as the motor is under less load.
Avoid Shifting Under Power
Even with a gear sensor, it’s best practice to avoid shifting gears while the motor is actively applying power. Develop the habit of briefly pausing your pedal input or throttle before initiating a gear change.
Shimano shifters on an e-bike handlebar, highlighting the rider interface for gear changes and control.
Shifting under full motor power puts significant stress on the chain and drivetrain components. You’ll likely hear a harsh “clunk” or grinding sound when shifting under power, indicating stress on the system. While a single instance might not cause immediate failure, repeated instances will accelerate wear and tear. Treat the gear sensor as a safety net, not a license to shift carelessly.
As you gain experience with your mid-drive e-bike, you’ll learn to anticipate gear changes and minimize the power interruption during shifts. You might even become skilled at shifting under power and relying on the gear sensor as a backup. However, especially when new to mid-drive e-bikes, err on the side of caution and pause power during shifts.
A useful technique for smooth shifting is to use brake lever motor cutoffs as a “clutch.” Slightly engage the brake lever just enough to activate the motor cutoff switch without actually applying the brakes. This momentarily interrupts motor power, allowing for smoother gear changes. Many e-bike brake levers are designed with this feature in mind. Magura MT5e levers, for example, have a hinged design that allows for motor cutoff activation with minimal lever movement.
Magura MT5e e-bike brake lever showing the hinge and pin mechanism for motor cutoff activation, facilitating smoother gear changes.
Optimize Chain Alignment
This is less critical for e-bikes under 1000W. Mid-drive motors operate efficiently across a broader RPM range than human cyclists. This can lead to riders using gears that result in extreme chain angles. While a mid-drive can function in gears that might be too low for comfortable human pedaling cadence, maintaining good chain alignment is crucial for drivetrain longevity, especially under high power.
Focus on using gears that keep the chain as straight as possible, particularly when applying significant motor power. On a multi-speed cassette, the middle gears generally offer the best chain alignment. When building a DIY mid-drive e-bike, consider this when selecting components. While a wide gear range is useful, prioritize gears that provide efficient motor operation and straight chain lines.
Whether you’ve built your e-bike or purchased it pre-assembled, avoid applying maximum torque when the chain is at extreme angles, either in the highest or lowest gears. On a regular bike, you can get away with more chain misalignment due to lower power input. However, with a 1500W+ mid-drive, a severely angled chain acts like a saw, rapidly wearing down chainrings and cassette cogs.
BBSHD mid-drive motor on a fat tire e-bike, illustrating a setup designed for durability and efficient power transfer in hilly environments.
If you’re building a DIY e-bike, identify any “problem gears” with poor chain alignment during initial test rides. Offset chainrings and chainring shims are available to improve chain alignment, and investing in these components can prevent premature drivetrain wear and potential breakdowns.
Avoid the Smallest Cog
A common recommendation in DIY e-bike circles is to avoid using the smallest cog on your cassette, typically the 11T cog. Frequent use of the smallest cog can lead to rapid wear or even breakage due to increased stress and chain angle. Even with durable steel cassettes, the smallest cogs are often made of aluminum alloy, which is more prone to cracking or accelerated wear under high torque.
It’s worth noting that individual small cogs (11T-15T) are readily available and relatively inexpensive to replace. They are often separate from the main cassette cluster, making replacement straightforward. So, while minimizing wear on small cogs is good practice, don’t be overly concerned about using them when necessary.
Beyond wear, the smallest cog often results in the worst chain alignment due to its outboard position on the cassette. This misalignment, combined with high torque, increases the risk of chain skipping, cog damage, or even chain breakage.
Furthermore, you might find that the smallest cog offers diminishing returns in terms of speed. With a powerful mid-drive, you may reach a point where shifting to the smallest cog doesn’t significantly increase your top speed, but instead puts unnecessary strain on the motor and drivetrain. Testing has shown that on some setups, the second or third smallest cog provides nearly the same top speed with better acceleration and less stress.
Build with Robust Components
If you purchased a production mid-drive e-bike, the components are likely chosen to withstand the motor’s power output. However, if you are building a DIY mid-drive e-bike, component selection is critical. A significant portion of mid-drive reliability issues stem from using components not rated for the increased stress of a powerful motor. Choosing robust chains, cassettes, chainrings, and even wheels is essential. Refer to dedicated resources on building durable mid-drive e-bikes for detailed guidance on component selection.
UPDATE: For in-depth information on building reliable mid-drive e-bikes and avoiding common mistakes, consult specialized guides focusing on component selection and best practices for DIY e-bike builds.
Riding is Easier Than it Sounds
While these guidelines might seem extensive, riding a mid-drive e-bike correctly quickly becomes intuitive. You won’t need to constantly think about shifting techniques. Mid-drive motors operate effectively across a wider gear range than human cyclists, naturally reducing the frequency of gear changes needed.
As a builder, selecting an appropriate front chainring size for your typical terrain is a key factor. Larger chainrings are suitable for flatter areas, while smaller chainrings are better for hilly terrain. Often, selecting a gear a couple of steps up from the lowest gear on your cassette and primarily staying in that range is sufficient for most riding. You can choose to prioritize a slightly lower top speed for ease of riding or utilize the full power and speed when desired.
Envoy cargo e-bike equipped with a mid-drive motor, designed for cargo hauling and adaptable to diverse riding conditions.
For example, on the California coast with varied terrain, frequent shifting is not necessary. Proper component selection and a slightly conservative gear choice minimize the need for constant gear changes while still providing ample power and range.
Conclusion
By choosing appropriate components and adopting smart riding habits, even high-powered mid-drive e-bikes can offer exceptional durability and longevity. While you will eventually need to replace wear items like chains and cassettes, the lifespan of these components is reasonable considering the mileage and enjoyment a mid-drive e-bike provides.
The appeal of high-powered mid-drives extends beyond just achieving high speeds on roads. While hub drives can also deliver high speeds, mid-drives offer superior climbing performance and control, especially off-road. For experienced mountain bikers, a mid-drive e-bike can transform uphill sections into exhilarating, skill-based challenges, blurring the lines between uphill and downhill riding. However, it’s crucial to recognize that riding a high-powered e-bike off-road, particularly at higher speeds, demands a higher level of skill and reaction time. It’s not simply about speed; it’s about control and safety, especially for less experienced riders venturing onto challenging terrain.
With mindful riding and appropriate maintenance, your mid-drive e-bike will provide countless miles of exhilarating and reliable performance. And most importantly, riding a mid-drive e-bike is incredibly fun!
