Studs refers to a class of tires that is raced in all 3 divisions. Street Studs are studded tires that are DOT approved for use on public roads. Pro Street Rally are winter rally ice racing tires and Pro Street Studs are custom-built according to the specifications in the rule book. Competition studs are 20mm and all of the tires are handmade. The traction from the studs adds more speed than the bare rubber classes. You can check the rule book for more specifications for these classes.