Essentially it’s the change in the distribution of the amount of weight that is on each of your four tires. The reason the distribution of weight can change is because the center of gravity (cg) of your car is above the road and the tractive forces of the tire on the road are at ground level.
Your car’s cg is a point that, were it suspended by a cable attached to the cg, it would balance perfectly. What’s more it would spin in any direction around the cg. You can consider the distance from the road surface to the cg as a lever arm‚ that inertia, acting on the cg of the car, uses to generate a torque or a twisting force. With a twisting force, known as a couple, the direction of that force is in opposite direction on each side of the circle.
For example, if torque is generated in a counter-clockwise direction, the force will take an upward direction at 3 o’clock and a downward direction at 9 o’clock. The effects of weight transfer are proportional to the lever arm‚ i.e., the height of the cg above the road.
Newton’s second law describes the relationship between objects and the application of force, and can be stated as follows: When a force is applied to your hot rod, the change in motion is proportional to the force divided by the mass of the car. This law is expressed by the famous equation F=ma, where F is a force, m is the mass of the car, and a is the acceleration, or change in velocity of the car. Newton’s second law explains why the world’s quickest cars are powerful and lightweight. A bigger force, i.e. more torque acting on less mass, i.e. vehicle weight, gives you more acceleration.
Newton’s third law says that every force acting on your car from another object, such as the road, is matched by an equal and opposite force on the object by the car. For example, braking causes the tires to push forward against the road with the road pushing back with equal force. As long as the tires stay on the car and in contact with the road, the road pushing back slows the car down. The weight transfer during braking comes about from the forces at the road surface because they are acting at a distance from the cg, imparting a torque and therefore a couple that lifts the rear of the car as it pushes the front of the car down