Wheel base

In both road and rail vehicles, the wheelbase is the distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is defined as the distance between the steering (front) axle and the centerpoint of the driving axle group. In the case of a tri-axle truck, the wheelbase would be the distance between the steering axle and a point midway between the two rear axles.

The wheelbase of a vehicle equals the distance between its front and rear wheels. At equilibrium, the total torque of the forces acting on a vehicle is zero. Therefore, the wheelbase is related to the force on each pair of tires by the following formula:

where ${\displaystyle F_{f}}$ is the force on the front tires, ${\displaystyle F_{r}}$ is the force on the rear tires, ${\displaystyle L}$ is the wheelbase, ${\displaystyle d_{r}}$ is the distance from the center of mass (CM) to the rear wheels, ${\displaystyle d_{f}}$ is the distance from the center of gravity to the front wheels (${\displaystyle d_{f}}$ + ${\displaystyle d_{r}}$ = ${\displaystyle L}$), ${\displaystyle m}$ is the mass of the vehicle, and ${\displaystyle g}$ is the gravity constant. So, for example, when a truck is loaded, its center of gravity shifts rearward and the force on the rear tire increases. The vehicle will ride lower. The amount the vehicle sinks will depend on counter acting forces like the size of the tires, tire pressure, and the stiffness 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:

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