It replaces the former class sysem where cars would be categorized based on their braking, top speed, acceleration, handling and (now removed) cornering statistics.
After the progression system, a majority of vehicles and items were made available for Credits, Premium cars were introduced, Lotus cars were no longer available for purchase, several upgrades were removed and added, the level/rank cap rose to rank 50, end-of-race rewards were also increased, and players were meant to level up to unlock cars and get better items and vehicles.
Stock cars are put into a specific level. Vehicles of lower performance would be unlocked sooner than that of the vehicles of the highest performance statistics which would be unlocked at the higher levels. For example, a car that would have under-average handling, good braking, bad acceleration and a bad top speed would be unlocked at the lower levels but not low enough to ignore the potential performance, whereas a car with over-average handling, under-average braking, good acceleration and a very high top speed would be unlocked in the higher ranks.
The pricing for cars that were for Credits were raised because of the new amounts of rewards in races. The same goes for E-Buck cars, except that those cars had lowered prices, as the value of E-Bucks was raised higher than that of before.
While most of the items in the Workshop were made available for purchase immediately via Credits, Upgrades in the workshop had to be unlocked at a specific amount of experience. All performance modifications were made available for purchase via Credits and varied in price depending on the car and its performance.