Formula Used
Total mass: m = bike mass + payload mass
Speed conversion: v = speed km/h ÷ 3.6
Acceleration: a = v ÷ acceleration time
Acceleration force: Fa = m × a
Grade force: Fg = m × g × sin(arctan(grade ÷ 100))
Rolling force: Fr = m × g × cos(angle) × Crr
Drag force: Fd = 0.5 × air density × Cd × area × v²
Peak force: F = Fa + Fg + Fr + Fd
Peak motor power: P = F × v ÷ efficiency × safety margin
Wheel torque: T = F × wheel radius
Current needed: I = peak motor power ÷ battery voltage
How To Use This Calculator
Enter the motorcycle mass first. Add rider, passenger, and luggage mass.
Set the target speed and acceleration time. Use realistic road values.
Add the steepest road grade expected during normal riding.
Enter tire rolling resistance, drag coefficient, and frontal area.
Set battery voltage, controller current, wheel radius, and gear ratio.
Add a safety margin for heat, voltage sag, hills, and rough roads.
Press the calculate button. Review peak power, continuous power, torque, and current.
Use CSV or PDF export to save the calculated result.
Choosing Motor Size
An electric motorcycle motor should match the whole ride, not only the top speed target. Mass, grade, wind drag, rolling loss, wheel size, and battery limits all change the final number. A light city bike may feel quick with a modest motor. A heavy build on steep roads needs far more peak power.
Why Peak Power Matters
Peak power is the short burst used for launches, hills, and passing. Continuous power is the level the motor can hold without overheating. Both numbers matter. The calculator estimates each value separately. This helps you avoid a motor that looks strong on paper but fades during real riding.
Main Forces
The tool adds acceleration force, climbing force, rolling resistance, and aerodynamic drag. Acceleration force depends on mass and time. Climbing force rises fast as grade increases. Drag becomes important at higher speeds. Rolling resistance is smaller, but it is always present.
Battery And Controller Check
A motor cannot deliver more than the battery and controller can support. The calculator compares required current with the controller limit. It also shows available electrical power. This check is useful before buying expensive parts. It can reveal weak links early.
Torque Planning
Torque decides how hard the bike pulls at the wheel. Wheel radius and gear reduction affect this value. A larger wheel needs more torque for the same force. A higher gear reduction gives more wheel torque, but lowers possible wheel speed.
Using The Result
Use the peak rating for acceleration and hills. Use the continuous rating for cruising and heat control. Add a safety margin for hot weather, luggage, rough tires, and battery voltage sag. Choose parts that exceed the calculated need. Never size a motor from speed alone. A balanced system rides better, runs cooler, and lasts longer.
Real World Notes
Real motorcycles face changing loads. Tire pressure, road surface, rider posture, and headwind can shift the answer. Use realistic inputs, not perfect lab values. Test the bike after assembly. Watch motor temperature, controller heat, and battery voltage during long climbs. If any part runs hot, reduce load or choose a larger component. Good sizing protects performance and safety. It also makes future upgrades easier, cheaper, and less wasteful later overall.
FAQs
What motor size do I need for an electric motorcycle?
It depends on mass, speed, acceleration, grade, drag, wheel radius, battery voltage, and controller current. This calculator estimates peak and continuous motor power from those inputs.
Is peak motor power the same as continuous power?
No. Peak power is a short burst for starts, hills, or passing. Continuous power is the level the motor can hold longer without overheating.
Why does road grade affect motor size?
A steeper grade adds climbing force. That force can become larger than rolling resistance and drag at low speeds, so hill riding often needs a larger motor.
Why is controller current included?
The controller limits how much current can reach the motor. Even a large motor may feel weak if the controller and battery cannot supply enough power.
What safety margin should I use?
A margin between 15% and 30% is common for practical estimates. Use more margin for steep roads, hot weather, heavy loads, or aggressive riding.
Does wheel size change torque demand?
Yes. A larger loaded wheel radius needs more torque to create the same pushing force at the road. Smaller wheels need less torque for equal force.
Can this calculator select a battery pack?
It helps estimate power and current demand. Battery selection also needs range, cell discharge rating, voltage sag, thermal limits, packaging, and safety planning.
Should I choose the exact calculated motor size?
No. Choose a motor and controller that exceed the calculated need. Extra capacity helps with heat, hills, voltage sag, tire changes, and future upgrades.