In physics, weight distribution effects how an object moves and collides with other objects. Here is the code I'm looking at to set Mass for the carObject.

body.Mass = mass;

Vector3 min, max;

car.Chassis.GetDims(out min, out max);

Vector3 sides = max - min;

float Ixx = (1.0f / 12.0f) * mass * (sides.Y * sides.Y + sides.Z * sides.Z);

float Iyy = (1.0f / 12.0f) * mass * (sides.X * sides.X + sides.Z * sides.Z);

float Izz = (1.0f / 12.0f) * mass * (sides.X * sides.X + sides.Y * sides.Y);

Matrix inertia = Matrix.Identity;

inertia.M11 = Ixx; inertia.M22 = Iyy; inertia.M33 = Izz;

If the bounds of the car is (4,2,2) and the Mass given is 100 the Ixx value is 66.66…, and the Iyy/Izz values are 166.66… Which make no sense to me at all. Shouldn't these values equal 100 when added up? I also don't get the arbitrary divide by 12.