If you turn on better driver skills (Don't go here if you haven't finished the game yet!. It's for the PS2 sorry...) the cars have hydraulics and you can make them jump up in the air when pushing down on the stick. Only cars which don't already have special abilities can jump though, so don't get any ideas about jumping a tank

You can end up doing really bizarre stunts because you can hit a proper ramp and use the jump cheat at the same time and end up going really far.

- Trevor