Once you've earned enough money, you'll definitely want to upgrade your car, too, because in the later races of each series, your opponents' cars will get faster. Choose from Engine, Drivetrain, Brakes, and Tire upgrades, each of which will give you an edge in your next race.
But here's where the freemium model comes into play. Every time you initiate an upgrade or maintenance task for your car, there's a wait time associated with each service. Changing your oil takes only 15 minutes, but more-complex upgrades can take hours to complete. Until the upgrade is complete, you cannot race with that car. You can choose to turn the game off for a little while to wait it out, or take the quick route of using your gold coins for immediate gratification. You only get a limited number of gold coins to start with, but you earn more as you move up in levels. Real Racing 3 lets you use real money to buy both in-game cash with which to buy new cars, and gold coins to speed up upgrades and repairs. I've found that using gold coins for some updates while waiting others out is not too painful, but your mileage may vary.
I have played and reviewed each Real Racing game since the first version came out in 2009, and it's the type of game that always has a place on my iOS devices. Before Electronic Arts bought Firemint, the game had a one-time-only purchase price, instead of the freemium model that you see with Real Racing 3.
I'm not sure why the company went with the freemium model, but I think it certainly detracts from the gameplay. While it's definitely more than a little frustrating to battle the time delays, I noticed it gets much easier when you've made enough money to buy more than one car. That way, when one car goes down for service, you can just switch to another car and complete races from a different series while you wait. The thing I don't like is that I have to come up with workarounds like this one just to keep playing -- a problem that a one-time purchase price would have eliminated.
Still, even with the freemium model, Real Racing 3 manages to continue holding the crown as the best racing game on a touch screen. Anyone who liked the earlier versions of the game or just likes speeding around a racetrack should download this game immediately.