where F f is the force on the front tires, F r is the force on the rear tires, L is the wheelbase, d r is the distance from the center of mass (CM) to the rear wheels, d f is the distance from the center of mass to the front wheels ( d f + d r = L ), m is the mass of the vehicle, and g is the gravity constant. So, for example, when a truck is loaded, its center of gravity shifts rearward and the force on the rear tires increases. The vehicle will then ride lower. The amount the vehicle sinks will depend on counter acting forces, like the size of the tires, tire pressure, and the spring rate of the suspension. If the vehicle is accelerating or decelerating, extra torque is placed on the rear or front tire respectively. The equation relating the wheelbase, height above the ground of the CM, and the force on each pair of tires becomes: