I beat the game with a few cars that may help you.

Grip
Audi54 maxed out

Drift
Nissian 350z maxed out

Drag
Dodge charger maxed out

Speed
911 turbo maxed out

I did use the cheat unlock all things to get 90,000 + each time you enter the game. You 1 go to carrer 2 go to code entry 3 enter unlock all things 4 enter any race 5 exit the race 6 go to the garage 7 you have 4 new cars 240sx colbalt gto viper 8 sell them all you get 90,000+ hope ot helps.

You can side flip by using a nitrous and hitting a hill's side

In the races there is a line of arowws they will help alot cause
You know wene you get to a sharp turn if you stay on it it slows
You down for you.