Mileage Points is a second form of currency, which is earned by completing races and challenges.
To tune a car, go to your garage, select a car and then choose settings. At the top of the screen, there should be an option called 'quick tune'. Depending on the value of the car, the two options Power and Weight will have a certain amount of tiers. You should use whatever car you start with, as the cheaper ones only have a total of four upgrades to buy, while high-end race cars will be very expensive to fully upgrade. For your cheap car, you will need roughly 1,500 Mileage Points to buy all upgrades, which you will easily obtain within a few races or tests.
