Need for Speed Underground Hints & Cheats

Enter the following at the main menu:

To unlock all visual upgrades for single and multiplayer mode, simply complete Underground mode.

Play through the game normally, and once you beat Samantha's Big Tease (#77), pick the Katana Unique Spoiler. Now, to get the Dual GT, trade in your car for a Peugot 206. Then, trade your car back to what you had and now your car has Dual GT as the spoiler. To switch back for the Katana Spoiler, just go to spoilers and scroll all the way to the end, and there's the Katana spoiler! Once you do this, you now will have both Katana and Dual GT in the customize ride from the main menu.

Certain cars can only fit so big of a rim. For example, the Miata can only fit 17s, but if you get a car like the Skyline put 20s on it and trade it in for the Miata. The Miata will now have the 20s that the Skyline had in it. Do not try to install any other rims on your new car because the rims will go back to the maximum sized allowed. You now can use rims that normaly wont fit .So now you no how to do it.