Podcast: Claus Fleischer from Bosch on E-Bike Power
Did you ever wonder where the power numbers on e-bikes come from? The rise of motor supported bikes has revolutionized cycling, blending human effort with electric power to redefine adventure, accessibility, and sustainability. In this episode of the TESTPILOT Podcast, Claus Fleischer, CEO at Bosch eBike Systems, unpacked the evolution of e-bike technology, regulatory challenges, and the delicate balance between innovation and preserving the "bicycle" status. Let’s explore the core concepts driving this revolution—and the physics behind the ride. The podcast and article below will go hand in hand to give you the perfect insight.
Enjoy 47 minutes of insights and thoughts on a topic that is hotter than ever in a challenging time in the bike industry.
From Automotive to Pedal Power: A Brief History
Bosch’s journey into e-bikes began not as an inventor but as a disruptor. In 2009, engineers fused automotive motor tech (like electric power steering), lithium-ion batteries from power tools, and sensor systems to create a professionalized e-bike ecosystem. The result? A corporate startup that transformed niche gadgets into robust, trail-ready machines. Early prototypes, Claus recalls, were comically crude—think "Daniel Düsentrieb" contraptions—but laid the groundwork for today’s sleek, smart systems.
By 2011, Bosch’s motors doubled torque (from 40–50 Nm to 100+ Nm), boosted battery capacity, and introduced features like anti-tuning safeguards. Yet Claus emphasizes: Innovation isn’t just about power—it’s about refining safety, efficiency, and user experience.
The Physics of E-Bikes: Breaking Down the Basics
If you look at the available bikes on the market you will run into a couple of key values to describe the motor. To understand e-bike performance, let’s demystify key terms and formulas. Stay with us, we will try to make it less boring than your ninth grade physics class:
1. Torque (Newton Meter, Nm)
Torque is the rotational force produced by the motor. Think of it as the "push" that helps you accelerate or climb hills. More torque can help you get the bike moving on lower cadence and heavier gears in a slower riding situation.
Formula:
Torque (τ) = Force (F) × Radius (r)
Example:
A motor delivering 85 Nm can apply 85 Newtons of force at a 1-meter lever arm.
Extended example for 100 Nm vs. 85 Nm:
A motor with 100 Nm could ride/feel similar to an 85 Nm motor, just 1 gear heavier. This is because the motor torque is transferred to the rear wheel via a shiftable gear ratio. This means if the rear sprocket (tooth size) is higher than the front, your rear wheel torque is amplified, meaning it is higher than the motor torque. If the rear sprocket is smaller (fewer teeth) than the front, then the torque at the rear wheel is reduced. The gear ratio is calculated by dividing the teeth at the cassette with the teeth at the front (e.g. 33t in the rear at 4th gear / 34t on the front chainring: 33/34 = 0,97.)
2. Cadence (RPM)
Cadence is the rider’s pedaling speed in revolutions per minute (RPM). Motors amplify your effort based on your input: The RPM and the torque you generate on the pedals, both get measured via a sensors. A motor with less torque will require higher RPM to deliver the same power as a motor with higher torque. If the motor provides more torque you can get the cranks moving even if you are in a (too) heavy gear or go with less RPM.
Higher cadence + higher torque = greater power output.
3. Wattage (Power)
Wattage measures the motor’s power output. It’s the product of torque and angular velocity (cadence).
Formula:
Power (P) = Torque (τ) × Angular Velocity (ω)*Angular Velocity (ω) = (2π × Cadence) / 60* (converts RPM to radians per second).
Example:
85 Nm torque at 80 RPM ≈ 711 watts.
4. Battery Capacity (Watt-hours, Wh)
Battery energy dictates range. A 500 Wh battery can theoretically deliver 500 watts for 1 hour. BOSCH has a calculator to give you an idea of what range and how many meters of climbing you can conquer. Click here.
Range Formula:
Range (km) = (Battery Wh × Efficiency) / (Power Demand in Wh/km)
*Efficiency (~80–90%) accounts for motor and terrain losses.
5. System Efficiency
Not all energy converts to motion. Heat and friction reduce output.
Formula:
Efficiency (%) = (Mechanical Power Output / Electrical Power Input) × 100
Are you still here? Do you need more practical examples?
The most confusing part for most riders is the difference between torque and wattage (power). E-bikes and their behavior in power delivery is defined by the correlation of these two. So let’s dive in one more time:
Wattage vs. Torque on an E-Bike
Torque (Newton Meters, Nm)
What it does:
Torque is the "muscle" that helps you accelerate or climb steep hills.
Example:
A bike with 80 Nm torque feels like a strong friend pushing you uphill—you accelerate quickly from a stoplight or conquer a 20% grade without pedaling harder.Wattage (Watts, W)
What it does:
The total power, combining torque and cadence (pedaling speed). Power (Watts) helps you maintain speed. The higher the power, the higher the achievable riding speed can be.
Simplified examples:500W Motor:
Like a marathon runner—sustains up to 25 km/h on flat roads efficiently, ideal for long commutes or gentle hills, but lacks brute force for steep climbs.750W Motor:
Like a sprinter—hits the max speed of 25 km/h quicker and effortlessly, powers through moderate hills (15% grades) and carries a heavier rider more easily, but drains batteries faster on sustained climbs.1000W Motor:
Like a powerlifter—muscles up 25 km/h even faster and conquers extreme terrain (25%+ grades) or heavy loads, but sacrifices range for raw power (battery drains much faster).
Assistance Factor
An e-bike is not working like a simple switch. Means pedaling does not turn the motor on with full power. There is sophisticated software behind it, which helps the human interact with how the power is delivered. Different modes help you adjust the needed power delivery, depending on where you are riding. You can also go into the app and customize how the modes work and make them fit your needs perfectly.
The so-called "assistance factor" plays a very relevant role in all of this.
Most drive units measure rider input power to request additional motor power. The assistance factor indicates how much additional motor power will be requested based on the measured rider input.
Example: 400% assistance
400% of assistance will request 400W motor power if the rider is putting in 100W. This combines to 500W of combined power.
Example: 200% assistance
If the rider is putting in 100W with 200% assistance, the requested motor power will be 200W. This combines to 300W of combined power.
To achieve 500W of combined power at 200% assistance, the rider will have to put in ~166W of power, receiving an additional 334W of motor power.
This means, higher assistance generally can lead to lower rider inputs, letting the motor do more work, which also drains the battery much quicker.
Also, the higher the assistance and the more power the motor provides, the smaller the control the rider has on riding.
Trade-Off:
If you listened already to the podcast with Claus, you understand, that everything comes with a trade-off. Higher wattage = more speed/power, but shorter range. You may choose your power based on terrain and priorities: endurance (500W), versatility (750W), or brute strength (1000W).
In the EU we are currently at 750W and try to do a better communication on what is still legal and considered a bicycle. People at BOSCH, ZIV and other institutions are working on this since years.
Key Takeaway:
High torque = Better for steep hills and quick acceleration.
High wattage = Better for maintaining speed over distance.
(Torque × Cadence = Wattage: More torque or faster pedaling = more power!)
Regulation vs. Innovation: Protecting the "Bicycle" Status
Klaus highlights a critical tension: Without industry-wide limits, e-bikes risk being classified as mopeds—requiring licenses, insurance, and banned from trails. Early regulations capped power at 250W continuous (EU) or 750W peak (U.S.), but gaps remain. Austria’s 600W peak limit once kept systems in check, but its repeal sparked a "Wild West" of marketing wars and as mentioned above we are now working with the 750W peak in the European Union.
Bosch advocates for responsible innovation:
Anti-tuning tech: Safeguards against speed hacks.
ABS systems: Prevent front-wheel skids or over-the-bar crashes.
IoT connectivity: The Coalition for Cyclist Safety envisions bikes communicating with cars and infrastructure to prevent collisions.
Claus argues limits fuel creativity: lighter motors, better heat management, smarter software. “Cranking catalog numbers isn’t innovation—it’s marketing.”
The Road Ahead: Where E-Bikes Are Heading
Smarter Integration:
Apps like Bosch’s Flow personalize assist ratios, blend physical/digital experiences, and even lock stolen bikes via digital twins.Battery Breakthroughs:
New chemistries and form factors promise lighter, longer-range packs.Safety Ecosystems:
ABS Pro, collision alerts, and theft tracking redefine rider security.
“E-bikes must stay a physical experience. Too much motor dominance turns active mobility into passive transport.” – Claus Fleischer
Conclusion: Freedom on Two Wheels
E-bikes are more than tech marvels—they’re gateways to exploration, exercise, and eco-friendly transit. As Bosch and regulators navigate power debates, the goal is clear: preserve the bicycle’s freedom while innovating responsibly. Whether you’re climbing alpine trails or commuting downtown, the future of e-bikes lies in balancing watts with wisdom.
“The moment you lose the status bicycle, you lose the joy.” —Claus Fleischer
Claus Fleischer on his way. This man lives and breathes e-bikes. Constantly testing and always innovating.
