How to adjust tire friction through physics material

I have made a car through video tutorials and now I’m trying to adjust its friction during the game.I have noticed the vehicle option in the physical material,but nothing happened to the tire friction after I changed the friction scale and applied the physical material to the mesh.
(Forgive my poor English, I’m a Chinese student.)

Do you still not see any difference if you change the Friction value under Physical Material section instead of Tire Friction Scale?

Yes, the material do looks ‘rougher’ after I changed Friction value, but my car sill moves when I set the value to zero. It only affects the friction when the wheel doesn’t roll.