Concept

# Wheelbase

Summary
In both road and rail vehicles, the wheelbase is the horizontal 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 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 is the force on the front tires, is the force on the rear tires, is the wheelbase, is the distance from the center of mass (CM) to the rear wheels, is the distance from the center of mass to the front wheels ( + = ), is the mass of the vehicle, and 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: where is the force on the front tires, is the force on the rear tires, is the distance from the CM to the rear wheels, is the distance from the CM to the front wheels, is the wheelbase, is the mass of the vehicle, is the acceleration of gravity (approx. 9.8 m/s2), is the height of the CM above the ground, is the acceleration (or deceleration if the value is negative). So, as is common experience, when the vehicle accelerates, the rear usually sinks and the front rises depending on the suspension. Likewise, when braking the front noses down and the rear rises.