Teams can replace drivers following the second event of the season as long as the replaced driver has not scored points. Racing at a lower IR can allow drivers to race against less skilled opponents and increase their IR through wins. iRatings, which determine license class, safety rating, and championships, are based on a driver's best races each week. As different car classes race together, drivers must follow safety rules and use common sense. Officials may prevent cars from starting if deemed a hazard or too slow in qualifying.