Rolling resistance. The rolling resistance of tractors is mainly caused by the deformation of tires and soil. Under the weight of the tractor, the tires were squashed and the soil was compacted. During the rolling process, the wheel is crushed and deformed in the circumferential direction at all parts where the tire contacts the ground, and the soil higher than the front of the wheel is pressed down, so that the soil is deformed to form ruts, that is, rolling resistance that prevents the wheel from rolling forward is generated. There are many factors that affect the rolling resistance, mainly related to the vertical load such as the firmness and humidity of the ground. For the same tractor, the rolling resistance will be different if the ground conditions are different. For example, when driving on asphalt cement or hard ground, if the rolling resistance is small, the tractor traction will be large. Under the same service conditions, the greater the weight added to the tire, the greater the vertical deformation of the soil and the greater the rolling resistance. Generally speaking, reducing the deformation of the tire itself and the vertical deformation of the soil is conducive to reducing the rolling resistance. If the tractor runs on soft ground, using low-pressure tires and increasing the supporting area of tires can reduce the vertical deformation of soil, reduce rolling resistance and improve traction.