Steps On How To Use Lateral Weight Transfer
For automobile enthusiasts and race engineers, the term “lateral weight transfer” is very familiar. But for the sake of those who are still getting to know this stuff, let us define what lateral weight transfer (LWT) means. Lateral weight transfer is defined as the amount of change on the vertical loads on the tires due to the lateral acceleration forced into the car’s center of gravity. In other words, it is the changes in the mechanical down-force and the grip of the car when breaking, accelerating or cornering. Its centrifugal force acts sideways at the Center of Gravity of the vehicle which is a direction away the corner’s center. These changes in mechanical down-force and grip can lead to losing the car’s traction. The Traction Control system of the vehicle optimizes grip and stability of the car while on the road during acceleration and wheel rotation. It reduces engine power which can stop wheel spin. As a result, the car can smoothly accelerate even on slippery surfaces.
Since weight transfer is a result of inertia and momentum, weight transfer cannot be eliminated; but the good thing is that it can be minimized. A reduced weight transfer would imply more retention in the car’s traction.
Source: http://www.motortrend.com/news/americas-best-handling-car/
It is important to know how to manipulate the lateral weight transfer. A deep understanding in weight transfer is the key to understanding the adjustments in our car for a maximum handling performance. The following are some of the tricks that can help change the total lateral weight transfer:
- Reducing the car’s ride height can lower down the Center of Gravity (CG).
- Changing wheels offsets or using wheel hub spacers can increase the car’s track width
With the items mentioned above, we can deduce that load transfer to be difficult to change once the car has been designed and built.
To help us get started, here are the steps on how to use lateral weight transfer:
Get the roll center height (front and back)
The car’s roll center is the point which the cornering forces in the suspension are reacted to the vehicle body. It is the point in which the force is transferred from the contact patches on the tire to the chassis. A car has 2 roll centers- the one found at the front and the other found at the rear. The roll center characteristics are important because it affects the roll center height. It can also cause camber changes due to its movement throughout the suspension travel.
Get the roll axis
When the car changes its direction, the body of the car pivots around the roll axis towards the opposing direction. This is a result of the centripetal force between the car’s center of gravity and its roll of axis.
A roll axis is the line which connects the 2 roll centers– front roll centers and roll centers in the rear. It is usually specified at the tire’s maximum load and inflation.
Get the Tire Static Load Radius
Static Load radius (SLR) indicates the vertical distance between the ground and the tire rotation axis.
Get the Tire Stiffness Rate
The vehicle’s ride comfort can be attributed to the tire’s overall stiffness. Most of the time, stiffer tires are harsh. The tire stiffness rate can be calculated via load-deflection, non-rolling and rolling of vertical free vibration, and non-rolling and rolling equilibrium of load-deflection. Among the five, load deflection is the simplest.
Get the Spring motion ratio
Motion ratio in suspension of a vehicle can be described as the level of shock travel for a given amount of wheel travel.
The car’s sprung weight can be calculated by subtracting the unsprung weight to the total weight. But before calculating the motion ratio, one should know the desired wheel travel first.
Get the ARB motion ratio
ARB, acronym for Anti Roll Bar, is a spring connected between the left and the right side of the car. It is a device which is used to control the amount of roll that a vehicle generates while cornering or over road irregularities. The amount of vehicle roll is dependent on the following factors:
- Lateral acceleration
- Center of gravity
- roll center
- track width
- spring rates
- damper settings
Get the track width
The vehicle’s track width has a significant impact on its cornering behavior. For example, a larger track width has an increased speed when driving in curves compared to those with smaller track width.
The track width is measured from tire center to tire center.
Get the Leaf spring spacing
Leaf springs are the oldest form of suspension as it possesses desirable features like forward bite, dampening, roll over steer, high lateral stiffness and high anti-squat percentage. Using the correct leaf spring spacing ensures proper ride high and more room for larger tires in your vehicle.
Get the Sprung mass CG height
There are different ways in calculating the Center of Gravity (CG) height but to alleviate the hassle of computing it, longacreracing.com has provided us with a program which can compute the center of gravity height. All you have to do is weigh the car and then raise the car at least 10 inches at the rear and weigh the front again. After getting the measurements, input the data in the program.
Get the Sprung mass weight distribution
Weight distribution is the apportioning of weight within a vehicle. Measuring it can be done by measuring the entire vehicle at once by placing the vehicle on a set of scales. This approach is what we call the total mass based approach.
Weight distribution is usually written in x/y where x is the percentage of the weight in the front and y is the percentage of the weight in the back. Handling automobile relies on gravity that is why weight distribution directly affects vehicle characteristics such as acceleration and traction.
Get the Roll Moment
In automobile, roll moment is the moment of inertia of the sprung mass. It is the linear distance between its roll center, which is at one end of the vehicle, and the concentration of mass at the end of the vehicle. It is the product of the sprung mass and the square of the distance between the vehicle’s roll center and its center of mass.
Get the Roll Stiffness rate per Roll Gradient
Roll stiffness refers to the resistance of springs that can be found in the suspension set in the body roll when the car goes around a corner. It is just equal to the roll stiffness in the rear and front suspension and it is expressed in torque.
Get the Total Lateral Load Transfer Distribution or TLLTD
The Total Lateral Load Transfer Distribution is the percentage of the roll gradient taken by the front suspension of the car.
Conclusion
The amount of lateral weight transfer can be easily computed by multiplying the centrifugal force to the CG height and dividing its product by the track width.
But aside from that, the items mentioned above are also some factors that we should consider for lateral weight transfer. Indeed, understanding and applying lateral weight transfer will require a lot of skills, practice in the track and familiarity in its process and of course, to the vehicle you are using. For professional car racers, these are only blocks on the road that need to be dealt to be able to achieve the greater price. Knowledge in lateral weight transfer can increase handling in our vehicle. Of course, safety always comes first.
