It is possible to put bigger/smaller rims on cars, because the size in inches changes from car to car, e.g. the Honda civic level 3 rims are 19", the Mazda rx7 level 3 are 20", etc.

Install the rims you like on the car you have. Then, trade your car in for a car that has rims of that level bigger or smaller than your car. Return to the rim customization screen and pick the same rims on that car. Although they already are installed, you must reinstall them for the game to register the size change. Clicking on next will simply ask you if you want to install the rims, although they already are, say yes. Then, go and trade your car back for what you had and it will keep the rim size you put on. On some cars, bigger rims will make them go through the fenders.

Having a hard time completing a drag race? Strip your car of every performance upgrade except handling and brakes. Your opponents will automatically do the same thing. This makes it easier to make a perfect shift everytime. This will work in all races except the ones that say you have to have a fast car.

First "draft" a car until your front bumper touches the opponent's rear bumper, then hit the Nitrous and your opponent's car will be flipped.

When you are in drift mode you can get some extra points for doing doughnuts. Hold one direction and the handbrake and gas and let go of the handbrake after a second. You'll just sit there and do doughnuts. This won't get you massive points but it's something.