To understand "what happens" to a moving vehicle, a little physics doesn't hurt. When we talk about "load transfers," we are talking about physical forces that act on vehicles during travel.
In a state of inertia – a car stopped or in rectilinear motion – the car has an optimal weight distribution between the front and rear axles. With every change in direction or speed (acceleration, braking, cornering), the vehicle is subjected to physical forces that cause continuous load transfers. That is, shifts in weight that alter the initial optimal balance. Each shift corresponds to a precise movement of the body relative to the wheels: pitch, roll, and yaw. Each movement corresponds to a consequent modification of tire grip. Let's look in more detail.
Pitch – during acceleration and braking, a longitudinal force acts on the front/rear axle of the car.
During acceleration, the car's nose lifts; the driver and passengers feel pressed against the seat. What happens? The load transfers to the rear axle: the increase in weight "presses" the tires to the ground, increasing grip. Conversely, the front axle – lightened – lifts.
During braking, the car's nose dips; the driver and passengers feel thrown forward. What happens? Most of the load shifts to the front axle, which becomes heavier and dips, improving tire grip. In more demanding braking, the weight can reach up to 80% on the front.
Roll – during changes in direction, a transverse dynamic force – centrifugal force – acts on the right/left side of the car.
The driver and passengers feel pulled towards the outside of the curve. What happens? Centrifugal force tends to move the suspended masses in the opposite direction to the center of the curve, i.e., outwards. Most of the weight rests on only two wheels: the car seems to lean on the asphalt towards the outside of the curve, while the inside lightens and lifts.
Yaw – is the rotational movement of a vehicle around its vertical axis, passing through its center of gravity: imagine inserting a pencil into the roof of our car and then rotating it. Unlike the other two, yaw does not occur during normal driving. Instead, it is the consequence of a loss of grip on the rear axle of the car: the vehicle skids and begins to rotate on itself.
Find out more about loss of grip, drift limit, and much more in our manual Sicuri al volante, available in yaw, print yaw, fordisu Amazon and in eBook and print versions on Lulu.
