For what it's worth, putting a smoother radius on the tire edge can make the traction rolling worse, depending on tire diameter and how high traction is. A squared off edge will chunk easier, but you will likely find it will help prevent traction rolling since the car can't roll as easily. This and the description of what front springs will do to car feel are the only places where my personal opinion differs from that of that 12th scale cheat sheet that people often post.