Here in rural Ohio we have the chip and seal type of roadways. Our chips are sharp angular crushed limestone. These are about 3/8” by 1/2” in size.
One time I ventured onto asphalt for a quarter mile. I couldn't believe how easy pedaling is - as far as tire friction. So you asphalt riders have it pretty easy as compared to country riders in the friction aspect. I would estimate that friction is reduced at least 25% on asphalt as compared to the chip and seal type roads.
On one of the bike forums we see an avatar of a young fellow grinning about his road rash. Trust me, …..if he slid on these chip type roads, he wouldn't be laughing. He would be in a hospital showing the ends of his ground down bones.
Packrat1947