A Car's Class is determined by the amount of Experience Points (XP) it has. Rookie Cars start with zero XP, and higher Factory Classes have more XP (see the table below). Cars gain additional XP from completing races, usually 0.05 XP per race. If a car does not finish a race (due to tire or engine problems, or crashing), it will not gain XP from that race. When a car is sold, XP and upgrades stay with the car.