Special Cars
There are some special cars in the game which you can unlock if you finish some races in the top two spots. To get the Gov'ner you'll have to come in first in every episode. Place first in Tiki Island as well to obtain the HW Prototype 12. To get the Jester you only need second place in the Zero Gravity episode, and second place in Spider Alley will win you the MS-T Suzuka.
Ultimate Special Car
The ultimate is an all-gold car. It is 24 carats and has gold rims. The only way to unlock this set of wheels is to complete the entire game. To do this, you'll have to get through six gaming areas.
Improve Your Car
When you want to upgrade your ride for performance or power, try these unlockables. To super-tune your car you need to finish first place in the Spider Alley episode. You only need second place to get power pipes for your car after racing in Lava Land. Second place in Tiki Island will get your car muscle tone.
Rims
To get all of the rims in the game you'll have to come in first in every single race. There are bonus rims as well if you try challenges within each area. For example, to get wheel rim 4 you'll need to win the Terror Saur race in the Jurassic Jam episode. You can get rim 5 there if you win the Dinosaur Boneyard race.