Studs refers to a class of tires that is raced in all 3 divisions. Street Studs are street legal studded tires that the competitor drives to the event on. Pro Street studs are 17mm and most tires are handmade or factory made and designed for ice racing. 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.