Each team has two cars in each race, which lasts for about 180 miles or 2 hours; whichever comes first. The cars must cary enough fuel to last the entire race, as there is no re-fueling allowed for safety reasons. In dry race conditions, two compounds of tires must be used according to the race rules. If if rains, the two compound rule is eliminated and any tires may be used. The team’s race strategists must figure out when to bring each team car in to change tires to get the best race results.