When you step into the Vehicle Dynamics section of PiCAD-Motor, you’re entering the bridge between motor design and real-world vehicle performance. This is where numbers, physics, and practical engineering meet. The motor is not just a standalone device—it is part of a bigger system that includes the battery, transmission, wheels, and vehicle body. Vehicle dynamics ensures that when you tweak motor design, you can instantly see how it impacts acceleration, gradeability, range, and overall efficiency.

Think of this as your digital proving ground. Instead of waiting to build a prototype and take it to a test track, you can simulate and validate the design in a matter of minutes.

The section is divided into input parameters (things you define about your vehicle and environment) and outputs (what PiCAD-Motor computes for you, such as torque-speed curves, power requirements, and range predictions).

 Power Source – The Heartbeat of Performance   

The very first input is the battery voltage (V), the electrical “pressure” that drives your motor.

• Battery voltage directly determines the maximum speed the motor runs at – higher the voltage, higher the RPM.

• Common voltage ranges vary based on the application:

• 24 – 72 V for low-speed two-wheelers

• 72 – 120 V for three-wheelers

• 100 – 300 V for small cars, hybrids

• 300 – 400+ V for cars and other heavier vehicles

 Motor to Vehicle Wheel – Connecting Power to the Road   

 Wheel Radius (m)   

This defines how power is transferred from motor to road. Larger wheels need more torque but allow the motor to spin slower, while smaller wheels do the opposite.

• Why it matters: The right wheel radius ensures that the motor doesn’t overwork or under perform.

• User workflow: You can either directly enter wheel radius or calculate it from tire specifications using PiCAD’s built-in calculator (like the 255/60R18 example).

• Real-world examples:

• Bikes and three-wheelers: 0.15 – 0.25 m

• Cars: 0.25 – 0.4 m

• Trucks and buses: 0.45 – 0.55 m

 Gear Ratio   

The torque of the motor is proportional to the current (I) supplied, and the losses are proportional to I². Hence, the motor is run at low torque and high RPM, requiring less current, and a gear is used to increase the torque at a reduced RPM, while maintaining the same power but higher efficiency.

Gear Efficiency (%)  

The gear efficiency for various types of gears in the transmission of power are given as follows can be chosen as per the application.

In Bikes: In bikes Spur gears are used.

In Cars: In cars helical gears is used due to their high contact ratio and smooth transmission.

 Frictional Forces – The Hidden Energy Consumers   

 Gross Vehicle Weight (GVW)   

Gross vehicle weight (GVW) is the total weight of a vehicle when fully loaded with passengers and/or cargo.

Common GVW ranges:

• Bikes and three-wheelers: 100 – 200 kg

• Three-wheelers: 600 – 1,000 kg

• Cars: 1,200 – 2,500 kg

• Trucks and buses: 3,500 – 7,500 kg

 Rolling Resistance Coefficient (μr)   

Friction force on a rolling tyre is proportional to the rolling resistance coefficient (𝜇r), which depends on the materials in contact. For pneumatic tyres, 𝜇r for different surfaces are given in the table below:

 Air Drag – Fighting Against the Wind   

Aerodynamic drag is often underestimated by new designers, but PiCAD makes it explicit.

Frontal Area (m²):

Frontal area is the area of the projection of the car on a plane perpendicular to air flow.

Common ranges of the area:

• Two-wheelers: 0.5 – 0.7 m²

• Three-wheelers: 1 – 1.5 m²

• Cars: 2 – 3 m²

• Trucks and buses: 3 – 4 m²

Drag Coefficient (Cd):

Aerodynamic force on a vehicle is proportional to the drag coefficient (Cd). The "boxier" the shape of the vehicle, the more the drag.

Drag coefficient ranges for vehicles:

• Bikes and three-wheelers: 0.6 – 0.9

• Cars, SUVs, vans: 0.25 – 0.45

• Trucks and buses: 0.5 – 0.7

 Rated Operating Point – Everyday Conditions   

Here, you define continuous gradient (road slope) and speed on gradient.

 Continuous gradient (road slope)

It is the average gradient at which the vehicle runs the most. In Indian roads the continuous gradient is lesser than 5°, as per regulations of NHAI (National Highways Authority of India.

Speed on Continuous Gradient

This is the speed at which the vehicle is designed to climb a slope over a journey that may last several hours.

 Acceleration – The Marketing Metric   

Acceleration defines the wow factor for consumers.

Target speed

Most manufacturers advertise how quickly the vehicle can ramp up from rest to a high speed. For instance, “zero to 100 Kmph in 10 seconds”.

Target time

This is the time taken to reach the target speed from rest.

 Gradeability – Climbing Power   

Gradeability determines how steep a slope your vehicle can climb.

Gradeability

Gradeability indicates the maximum incline that the vehicle can climb in a short burst (of about 10-sec). In Indian roads, the maximum incline is 12.4°.

Length of Grade

As per the test procedure defined by ARAI (Automobile Research Association of India), the vehicle is expected to cover a length of 15m plus its wheelbase, on fully loaded condition (max GVW), to demonstrate its gradeability. The vehicle should start from rest and cover the specified distance without any stops on the way.

The wheelbase of 2 and 3 wheeler is generally 2m. The wheelbase for a four-wheeler can vary from around 2.5 to 3.5 meters.

Time to cross grade from rest  

This is the time in which we wish to cross the specified grade-length, starting from rest. Too short a time would imply a higher peak-torque demand from the motor, while too long a time runs the risk of motor over-heating. A time duration of 10 to 15 seconds is recommended.

Power Ratio  

It is a ratio that compares the peak power (maximum power output of an electric motor) to the power at its maximum gradient (the power output of the vehicle when it is climbing a steep incline or facing a challenging terrain where the gradient is at its highest point).

 Top Speed – Highways & Beyond   

The maximum vehicle speed that the vehicle is designed to achieve on a level road. Usually, it is around 100 to 200kmph.

 Simulation Outputs – Turning Inputs into Insights   

Once you define parameters, PiCAD generates outputs in three categories:

 1. Motor Specifications   

• Torque vs. Speed curve

• Power vs. Speed curve

• Key metrics table:

• Peak Torque

• Peak Power @ Torque

• Peak Speed

• No Load Speed

• Rated Operating Point

 2. Drive Specifications & Motor Constants   

• Voltage (V), Current (A)

• Ke (Vs/rad, V/Krpm)

• Kt (Nm/A)

• RMS Current