Some cars are in a special collection that can earn you rewards! That is called a collection, my folks. When you buy a car, it may or may not be part of a collection. Most of the time, it will be in one collection. Some are in more than one, some are in three, or more. If you fill all the cars in the collection, you get an exclusive reward for filling that collection. After that, another collection starts with the same cars in that collection, except they need to be completely MAXed. If you MAX all those cars, you get DOUBLE the rewards that you do compared to the normal collection. You need to get all cars in the collection before unlocking the MAXed collection.