The road resistance is one of the constant driving resistances, always present, but not, e.g., like the wind resistance, which increases rapidly with the driving speed. This makes it difficult to reduce.
In this case, not only the friction between the road and the tyre plays a part, but also the movement within the tyre (churning). The tyre is, depending on internal pressure, burden and dimension, more or less compressed when rolling on the road surface. Even the driving speed is relevant, because at higher speeds, the dynamic wheel radius increases. Actually, one must also add the losses through friction, which e.g., rims with a lot of openings or tyres with a chunky tread profile cause when interacting with the surrounding air. Not to mention, in particular, the air-flow to cool the brakes. Just as one can hear the different noises that the same vehicle causes on various road surfaces, is, in these cases, also the road resistance different. This has to do with the road itself, but also with the surface covering, e.g., black ice. The previously mentioned factors can be slightly influenced by the driver, the following, hardly at all. They are partly dependent on the construction, and partly on the maintenance requirements. Belonging to this is the rolling friction in the sometimes adjustable wheel bearings and the friction within the brakes. The question here is, how much play does the brake disc or drum need, to prevent the brakes dragging shortly after the braking operation or permanently? Some modern braking systems also use the drag to keep the discs free of water.