The Bafang M620 Ultra promised to be the ultimate high-power eMTB motor with 160Nm of torque and 1000W of raw grunt. After analyzing extensive user reports, controller burning incidents, and long-term reliability data, this motor emerges as a paradox of impressive power wrapped in frustrating compromises. While it delivers unmatched torque and modification potential, the M620 carries reliability demons that Bafang has struggled to exorcise.
The Power Beast That Roars Too Loud
Originally introduced in 2018 as the G510, the motor evolved to the M620 designation after Bafang swapped plastic gears for steel ones to handle the abuse from power-hungry users pushing these motors beyond their limits. This change solved the gear failure problem but introduced new issues that persist in the latest models. The M620 Ultra delivers on its power promises with brutal efficiency. This 6.7kg monster produces 160Nm of torque from its 1000W motor, with peak outputs reaching 1500W and modification potential extending to 3000W. However, all that power comes with an acoustic penalty that makes subtle trail riding impossible.
The characteristic “watt crunching basso-whine” has become an M620 trademark that riders either embrace or endure. Unlike the refined whisper of premium European motors, the Ultra announces its presence with a coarse-toothed buzz and metallic engagement sounds that penetrate helmet and headphones alike. This noise signature stems from the steel gear upgrade that replaced early plastic gears, which failed catastrophically under normal 30A operation.
The Weight Penalty
At 6.7kg, the M620 weighs double that of premium competitors. This mass penalty affects bike agility, climbing responsiveness, and transportation logistics. While the weight sits low in the frame, riders notice the difference immediately when lifting bikes or navigating technical terrain requiring quick direction changes.
Testing reveals that the motor’s thermal management struggles under sustained high-power operation. The compact housing cannot dissipate heat effectively when modified controllers push beyond the 1000W design limit, leading to power reduction precisely when maximum output is needed most. This thermal sensitivity becomes pronounced during extended climbing sessions or aggressive trail riding.
Technical Reality: The G510/M620 Evolution
The M620 evolved from the original G510 through necessity rather than planning. Early plastic gear failures forced Bafang’s hand, resulting in steel gear upgrades that solved durability issues while introducing new noise and weight penalties. The steel gear upgrade addressed early reliability concerns but introduced new complexities. While more durable than the failed plastic predecessors, the steel gears require precise manufacturing tolerances and contribute significantly to the motor’s characteristic noise profile. Recent higher tooth-count gear options promise quieter operation but at additional cost and complexity.
M620 Ultra Specifications Breakdown
Reality Check: The M620 isn’t a simple upgrade from popular motors like the BBSHD. It’s a fundamentally different beast requiring special frames, specialized knowledge, and a tolerance for maintenance that many conversion enthusiasts underestimate.
The Controller Burning Epidemic
Perhaps the most serious issue plaguing the M620 involves systematic controller failures that have affected multiple users across different markets. These failures follow predictable patterns that suggest fundamental design vulnerabilities rather than isolated incidents.
The controller burning phenomenon typically occurs during normal operation, often triggered by mechanical stress events like hard landings or chain derailments. Multiple users report controllers burning in identical locations on the circuit board, suggesting a systematic weak point in the design. More concerning, burned displays can create a chain reaction, immediately destroying replacement controllers when reconnected.
The Display-Controller Death Spiral
Widespread
Predictable
Expensive
Third-party displays appear particularly susceptible to this failure mode, with Eggrider and 500C displays frequently implicated in controller burning incidents. The exact failure mechanism remains unclear, but voltage spikes or communication protocol mismatches seem to create cascading failures that affect both display and motor controller.
Honest Assessment: Raw Power vs Practical Compromises
The M620’s impressive specs translate to real performance gains in specific scenarios, but the motor’s character reveals itself through daily use. Understanding these performance patterns helps determine if the M620 fits your actual riding needs.
Where the M620 Excels
Hill Climbing Performance
The M620’s 170Nm torque makes short work of steep grades that would challenge other motors. Users report climbing 15-20% grades with heavy loads without breaking a sweat. The torque sensing provides natural power delivery that matches your effort level.
Heavy Load Capacity
Designed for cargo bikes and fat bikes, the M620 handles heavy loads better than any other conversion motor. Whether you’re carrying groceries, tools, or camping gear, the motor provides consistent power delivery without strain.
Tuning Potential
For power enthusiasts, the M620 offers exceptional modification potential. Users report pushing motors beyond 2000W with aftermarket controllers. The steel gear design was specifically created to handle this abuse.
Where the M620 Struggles
Controller Burnouts
Multiple users report identical controller failures, often after installing EggRider V2 displays. The failure occurs at specific connection points, suggesting a design vulnerability. One user reported burning through three controllers before identifying the EggRider as the culprit.
Torque Sensor Failures
Forum reports indicate torque sensor failures around 6,000 miles of use. When this happens, the motor loses all pedal assist function but throttle continues to work. Replacement sensors cost $200-400 and require motor disassembly.
Maintenance Demands
The M620 requires regreasing every 1,500 miles according to experienced users. This isn’t mentioned in Bafang’s documentation but appears necessary for longevity. Users who skip this maintenance report gear noise and premature wear.
Programming Complexity
CANBUS versions offer minimal programming options despite marketing claims. Users report being able to change only wheel size and speed limits. UART versions are programmable but many users struggle with communication errors and require specialized cables.
The Maintenance Trap You Can’t Avoid
Unlike premium motors designed for minimal intervention, the M620 demands regular maintenance that many riders discover only after problems develop. The 1500-mile grease replacement interval isn’t optional—it’s essential for preventing catastrophic wear and noise development.
Maintenance Requirements Most Don’t Expect
The maintenance complexity extends beyond simple grease replacement. Any gear changes require recalibration using expensive diagnostic equipment that most shops don’t possess. This creates service bottlenecks and forces riders into dealer dependency that contradicts Bafang’s traditional DIY-friendly approach.
Neglecting maintenance schedules leads to rapid deterioration. Users report dramatic noise increases and eventual bearing failures when maintenance intervals are exceeded. The motor’s high power output accelerates wear patterns, making preventive maintenance critical rather than optional.
Programming: Power vs Accessibility
The M620’s programming capabilities reveal the stark divide between UART and CAN bus versions. UART motors offer extensive customization options that can transform motor behavior, while CAN bus versions provide limited adjustment parameters that frustrate enthusiasts seeking optimization.
UART Advantages
UART versions provide extensive programming flexibility, allowing power curve adjustments, torque sensor calibration, and power limits that can optimize motor behavior for specific applications. However, UART motors are becoming increasingly rare as Bafang transitions to CAN bus systems.
CAN Bus Limitations
CAN bus versions offer minimal programming options without expensive dealer tools. Basic parameters like assist levels can be adjusted, but fundamental motor behavior remains locked. This restriction particularly affects riders wanting to address controller refinement issues.
Stock Programming Issues
Many users describe stock programming as “terrible,” with power fluctuations, delays, and overruns that require custom tuning to resolve. Poor factory calibration often masks the motor’s true potential, creating disappointing initial experiences.
Modification Potential
With proper programming, the M620 can reach 3000W+ outputs that create “ejection seat” acceleration. However, this power level destroys drivetrain components rapidly, requiring upgraded chains, cassettes, and chainrings to handle the stress.
UART vs CANBUS: The Real Differences
| Feature | UART Version | CANBUS Version |
|---|---|---|
| Programmability | Full access with Bafang Configuration Tool | Limited to speed and wheel size adjustments |
| Reliability | More controller failures reported | Better overall reliability |
| Customization | Complete power curve adjustment | Factory settings only |
| Battery Compatibility | Works with any appropriate voltage battery | May require specific Bafang batteries |
| Troubleshooting | Detailed diagnostic access | Limited diagnostic information |
| Future Support | Being phased out by Bafang | Current production standard |
The UART Dilemma: Forum users consistently report that early UART models were problematic, with some describing them as “no good.” However, UART versions offer the programmability that enthusiasts want. If you choose UART, buy from a reputable dealer and budget for potential controller replacement.
Power Delivery: Brutal Efficiency vs Refined Control
The M620’s approach to power delivery prioritizes maximum output over refined modulation. This philosophy becomes apparent during aggressive acceleration where the motor can produce “ejection seat” bursts that stress both rider and drivetrain components.
Power Delivery Characteristics
Usable
Effective
Destructive
At maximum settings, the motor produces close to 300Nm of torque that can snap chains, destroy chainrings, and shred cassette cogs. This power level requires upgraded drivetrain components specifically designed for high-stress applications, significantly increasing total system cost.
The motor’s thermal behavior under sustained load reveals design limitations. Extended high-power operation causes heat buildup that triggers thermal protection, reducing output when maximum power is most needed. This thermal limitation affects climbing performance and extended trail riding scenarios.
M620 vs The Competition: How It Really Stacks Up
Comparing the M620 to other high-performance motors reveals where it excels and where alternatives might serve you better. Real performance often differs significantly from specification sheets.
Performance Comparison Matrix
The comparison reveals the M620’s position as the raw power option that sacrifices refinement for output. While it dominates torque specifications, the weight, noise, and reliability penalties become significant when compared to premium alternatives. The programming advantage only applies to increasingly rare UART versions.
The BBSHD Alternative: Many users who researched the M620 ultimately chose the BBSHD for its proven reliability, quieter operation, and universal frame compatibility. The BBSHD delivers 80% of the M620’s performance with 20% of the hassles.
Should You Buy an M620 Ultra? Decision Framework
The M620 isn’t universally good or bad. It excels in specific scenarios but demands compromises that many riders find unacceptable. Use this framework to determine if the M620 aligns with your actual needs and constraints.
Consider the M620 Ultra If
- You regularly carry heavy loads (50+ lbs) or pull trailers
- Your daily routes include grades steeper than 15%
- You have access to a compatible frame or budget for custom framebuilding
- You’re comfortable with complex maintenance schedules
- Maximum power output is your primary concern
- You have mechanical skills or access to knowledgeable service
Avoid the M620 Ultra If
- You want a quiet, unobtrusive motor
- You’re converting an existing bike (frame compatibility issues)
- You prefer simple, reliable systems over maximum performance
- You’re new to e-bikes or electric systems
- You want minimal maintenance requirements
- Budget is a primary concern (higher purchase and ownership costs)
Bafang M620 Ultra System
Final Verdict: Power vs Practicality
The Bafang M620 Ultra represents a compelling but flawed vision of high-power eMTB performance. While delivering unmatched torque output and modification potential, this motor demands compromises that many riders discover only after purchase. The controller burning epidemic, mandatory maintenance requirements, and noise levels create ownership experiences that can frustrate despite the impressive power delivery.
This motor succeeds when riders prioritize raw power over refinement and accept the associated maintenance burden. However, the combination of reliability issues, weight penalties, and service complexity makes it a risky choice for riders seeking worry-free performance.
If Maximum Power Is Your Priority: The M620 Ultra delivers unmatched torque and power output. For cargo bikes, delivery applications, or extreme terrain, nothing else comes close. Budget for the additional complexity, noise, and maintenance requirements.
If You Want Balanced Performance: The BBSHD offers 80% of the M620’s performance with significantly better reliability, quieter operation, and universal compatibility. For most riders, this represents the better value proposition.
Final Reality Check: The M620 Ultra remains the ultimate choice for riders who prioritize power above all else and accept the associated compromises. However, the controller reliability issues and maintenance requirements make it unsuitable for riders seeking the refined, worry-free experience that premium European motors provide. Choose wisely, as this motor demands commitment to its particular philosophy of brute force over finesse.
