When you start driving career, buy Malice as your first car, it's fastest of the 3 starting cars.
You don't really need any upgrades for it.

Drive the 2 first cups and try to win them in 1st place, it's very easy.

Then drive the derby and the time trial.

After you have completed those 4 events, you should have at least 7000CR (money). Blaster XL costs 8000CR but you can get 1000CR by just crashing into others and having the fastest lap in the 2 cups. When you have 8000CR just buy Blaster XL and go race with it, you don't really need any other cars. Just keep upgrading or don't upgrade it at all, it's faster and stronger than Malice even without upgrades.

This class is really easy, but you need a lot of money for it. After you complete derby class, you should have at least 60000CR, unless you spent all of your money on upgrades. If you don't have 60000CR, just go play more derby class and earn some more money.

After you have 60000CR, buy Insetta! (YOU DON'T HAVE INSETTA UNLOCKED IF YOU DON'T GET GOLD IN CRASH ALLEY EVENT IN CARNAGE MODE!!!)
After you get Insetta just go race, you don't really need any upgrades for it. Insetta is a very fast car, 1 of the fastest in FOUC.

So you just drive the whole Race Class with Insetta and SAVE money for the Street Class.

Once you have completed Derby and Race classes, go and buy Road King! (AND AGAIN YOU DON'T HAVE ROAD KING UNLOCKED UNTIL YOU HAVE GOLD IN MOTOR RACEWAY 2 EVENT IN CARNAGE MODE!!!)

Road King is the fastest of FOUC cars (excluding BONUS cars) but you may want to upgrade it to have better handling and durability, because especially the handling can be a bit tricky for some people.

You may want to drive the race cups with Road King and buy f.e Canyon for the derby events.

When you get to this part of career mode, you most likely have enough money for anything really. You can buy Grinder for the derby finals cup and use the cars you already have for the other cups.


So this is how I have completed the Career Mode every time with ease.

-The Derby Class may be a bit hard for some people with the not-too-fast Blaster XL but you may go and buy some upgrades for it.
-The Race Class should be easy peasy with Insetta since it's fast as a bullet.
-Street Class should be about the same as Race Class because Road King beats everyone. Even if you have some problems with keeping the car under control, the speed makes up for it.
-Grand Finals is as easy as the others. Just buy a new fast derby class car for the derby cup and use your older cars for the other cups.