What are the best methods to measure and optimize the center of gravity of electric and hybrid vehicles?

The center of gravity (CG) of a vehicle is the point where the weight of the vehicle is balanced in all directions. It affects the vehicle's stability, handling, performance, and safety. Electric and hybrid vehicles have different weight distribution and CG than conventional vehicles, due to the presence of battery packs, electric motors, and other components. In this article, you will learn what are the best methods to measure and optimize the CG of electric and hybrid vehicles.

1 Why CG matters

The CG of a vehicle influences how it behaves on the road, especially when cornering, braking, or accelerating. A lower and more central CG improves the vehicle's agility, responsiveness, and stability, as it reduces the body roll, pitch, and yaw motions. A higher and more offset CG increases the risk of rollover, understeer, or oversteer, as it creates more lateral and longitudinal forces on the tires and suspension. Therefore, it is important to design and optimize the CG of electric and hybrid vehicles to achieve the desired performance and safety characteristics.

Add your perspective

2 How to measure CG

There are several methods to measure the CG of a vehicle, depending on the level of accuracy and complexity required. One of the simplest methods is to use a set of scales and a level platform to measure the weight and height of each wheel. By applying some basic physics equations, the CG location can be calculated from the weight distribution and the wheelbase and track dimensions. Another method is to use a tilt table or a ramp to measure the angle at which the vehicle starts to tip over. By knowing the vehicle's weight and dimensions, the CG height can be determined from the tilt angle. A more advanced method is to use a kinematic and compliance (K&C) test rig, which can measure the CG location and the suspension characteristics of the vehicle under various loading conditions.

Add your perspective

Chris Coker

Technical Specialist, Vehicle Dynamics Simulation - Enable Engineers to Produce Durable, Robust Products That Exceed Performance Criteria
Report contribution
K&C test rigs are not typically used to measure CG of vehicles. In the automotive industry, there are inertial rigs that can do this quite well, and calculate inertia as well.

Like
Chris Coker

Technical Specialist, Vehicle Dynamics Simulation - Enable Engineers to Produce Durable, Robust Products That Exceed Performance Criteria
Report contribution
One thing I found helpful in making these kinds of measurements is ensuring you have enough resolution on your scales to get an accurate CG calculation. The weight transfer can be very subtle, and if you don't have enough resolution, you have to lift one vehicle very high. So, it's important to have good quality scales, with adequate resolution.

Like

3 How to optimize CG

The CG of a vehicle can be optimized by adjusting the mass and position of the components that affect the weight distribution. For electric and hybrid vehicles, the main components are the battery pack, the electric motors, and the fuel tank (if any). The battery pack is usually the heaviest and most bulky component, so its location has a significant impact on the CG. Ideally, the battery pack should be placed as low and as central as possible, to lower and balance the CG. However, this may not be feasible due to packaging constraints, thermal management issues, or crash safety requirements. Therefore, trade-offs and compromises may be necessary to find the optimal battery location. The electric motors can also be placed in different locations, such as in the front, rear, or center of the vehicle, or in each wheel hub. The location of the electric motors affects not only the CG, but also the powertrain configuration and the torque distribution. The fuel tank, if present, can also be moved or resized to optimize the CG, but this may affect the range and efficiency of the vehicle.

Add your perspective

4 How to test CG

The CG of a vehicle can be tested by performing various dynamic tests on a track or a simulator. These tests can evaluate how the CG affects the vehicle's handling, stability, and performance under different driving scenarios. Some of the common tests are steady-state circular test, slalom test, lane change test, brake test, and acceleration test. These tests can measure parameters such as lateral acceleration, yaw rate, steering angle, braking distance, and acceleration time, which can indicate the vehicle's behavior and response to the driver's inputs. By comparing the test results with the CG measurements and the design objectives, the vehicle's dynamics can be analyzed and improved.

Add your perspective

5 How to model CG

The CG of a vehicle can also be modeled by using software tools and mathematical models that simulate the vehicle's dynamics and kinematics. These tools can help to design and optimize the CG of electric and hybrid vehicles in the early stages of development, before building and testing physical prototypes. Some of the software tools that can model the CG of electric and hybrid vehicles are Adams Car, CarSim, Simulink, and MATLAB. These tools can create virtual models of the vehicle's components, such as the chassis, suspension, tires, battery, electric motors, and fuel tank, and assign them mass and position properties. Then, these tools can run simulations of various driving scenarios, such as cornering, braking, or accelerating, and generate outputs such as forces, moments, velocities, accelerations, and trajectories. These outputs can help to evaluate and optimize the CG of electric and hybrid vehicles.

Add your perspective

Michael Peck

Managing Director specializing in forensic technologies and vehicle dynamics
(edited)
Report contribution
An insightful read about vehicle design considerations. There are other factors that need consideration, I.e. those that affect the drivers command and control over their vehicle. For example, and in simple terms, a polar moment that enables a vehicle to rotate efficiently around its centre of mass is generally a preserve of race cars. Whilst desirable in theory, highly efficient steering response has higher yaw rates that can be difficult for a ‘conventional’ driver to handle during evasive manoeuvres. It is equally the case that were mass is reduced at the front and rear of vehicles and is brought inboard of the axles, inertial damping characteristics are also reduced which is desirable for race vehicles but less so for road drivers.

Like

What are the best methods to measure and optimize the center of gravity of electric and hybrid vehicles?

1

2

3

4

5

1 Why CG matters

2 How to measure CG

3 How to optimize CG

4 How to test CG

5 How to model CG

Vehicle Dynamics

Rate this article

Thanks for your feedback

More articles on Vehicle Dynamics

More relevant reading