The driving ability is driven by the power of the internal combustion engine through the transmission system, so that the driving wheel obtains the driving torque Mk, and the driving wheel obtains the driving torque to give the ground a small, backward horizontal force (tangent force) through the tire pattern and tire surface.
The horizontal force Pk that has the same driving force and the opposite direction is applied. This Pk force is the driving force that pushes the tractor forward (also called the propulsion force). When the driving force Pk is sufficient to overcome the forward rolling resistance of the front and rear wheels and the traction resistance of the agricultural implements, the tractor will move forward. If the driving wheel is set off the ground, that is, the driving force Pk is equal to zero, the driving wheel can only idle on the spot and the tractor cannot travel; if the sum of rolling resistance and traction resistance is greater than the driving force Pk, the tractor cannot travel. It can be seen that the driving of the wheeled tractor is realized by the interaction between the driving torque driving wheels and the ground, and the driving force is greater than the sum of rolling resistance and traction resistance.