Unlock Race Mode:
Complete all missions in story mode.
Unlock More Free Ride Cars:
Break into a car in story mode to unlock it in free ride mode.
Unlock Bigfoot Truck in Free Ride:
Win first place in all racing championship mode races.
Free Ride Mode Car Selection:
When you start free ride mode, simply drive forward a bit, then reverse back where you started. A car selection screen will appear where you can select any available car.