How a four-wheel tractor works
A tractor is able to move forward due to the power from the internal combustion engine being transmitted through the drivetrain system, which provides the drive wheels with driving torque Mk. The drive wheels, having obtained the driving torque, then apply small, backward horizontal forces (tangential forces) to the ground through the tread patterns and surfaces of the tires. In response, the ground exerts an equal but opposite horizontal reaction force Pk. This Pk reaction force is the driving force that propels the tractor forward. (also known as propulsive force). When the driving force Pk is sufficient to overcome the rolling resistance of the front and rear wheels and the traction resistance of the attached agricultural implements, the tractor moves forward. If the drive wheels are lifted off the ground, i.e., the driving force Pk is zero, the drive wheels can only spin in place, and the tractor cannot move; if the sum of rolling resistance and traction resistance exceeds the driving force Pk, the tractor also cannot move. As can be seen, the movement of a wheeled tractor is achieved through the interaction between the driving torque and the ground, and the driving force must be greater than the sum of rolling resistance and traction resistance. Below, we will analyze the main factors affecting tractor movement.
