Rolling Friction

Rolling friction is the resistive force that slows down the motion of a rolling ball or wheel. This frictional force is typically a combination of several friction forces and is at the point of contact with the ground or other surface. When the materials are both hard, static friction and molecular friction slow down the rolling. When the wheel or tire is soft, its distortion slows down the motion. When the other surface is soft, the plowing effect is a major force in slowing the motion. The coefficient of rolling friction is determined experimentally.

static friction
The surface of the wheel and what it is rolling on are not perfectly smooth. They have irregularities. In sliding friction, this surface roughness is the reason for the static and kinetic resistance to motion. Although the wheel is not sliding, the surface roughness causes a "jiggle" when the wheel is rolling. The resistance from this movement is close to the point where static friction transitions to kinetic friction.
Treads
If the wheel or tire has treads or grooves with sharp edges, those edges add to the static friction when they come into contact with the ground or other surface. Treads can help to prevent spinning the tire when the force from the torque becomes larger than the static friction. They also help prevent skids when braking.
Molecular friction
Molecular friction is caused by the molecular attraction or adhesion of the materials. It is like a "stickiness" factor. When materials are pushed together, molecular forces try to prevent them from being pulled apart. This can be seen in highly polished metals and certain materials such as rubber. As an extreme example, you could put double-sided tape on the rim of a wheel and see the resistance to rolling from the sticky tape.
Wheel is soft
When a wheel or tire is relatively soft and can be easily deformed, the resulting friction is a form of plowing friction. The deformation of the tire takes up energy that would be used to roll the wheel. Deformation is the greatest factor in rolling friction of tires or wheels made of soft materials.
Increasing tire pressure is a way to reduce rolling friction in an automobile or bicycle.
Surface is soft
When the ground or other surface is relatively soft, the major source of friction comes from the plowing effect. The wheel sinks into the soft material and must push or plow its way through. Although rolling is more effective than sliding an object in a soft material, it still requires a substantial effort.
Trying to ride a bicycle through soft dirt is an example of the effect of rolling friction on a soft surface.
Although treads on the wheel or tire will help to move the tire through the soft material, they do not contribute much rolling friction force in resisting the motion.
Both are soft
Interestingly, you can drive a vehicle through soft dirt easier if its tires have less air. The deformation of the tire improves traction.

Reaction:
Rolling friction is the force that slows down the motion of a rolling wheel. This frictional force is typically a combination of several friction forces at the point of contact with the ground. When the materials are both hard, static friction and molecular friction slow down the rolling. When the wheel or tire is soft, its distortion slows down the motion. When the other surface is soft, the plowing effect is a major force in slowing the motion. draft