Extra cars:
Start a new race. Choose the "Begin Career" selection. Enter GO_BEARS! 
(for stock cars) or GO_BRUINS! (for formula one cars) at the "Register" 
screen. Note: "_" indicates a space. 

In-race car modifications:
Pause the game during a race. Enter the "Race Statistics" screen. 
Hold L1 + L2 + R1 + R2 + X + Circle + Select. A car editor menu with the 
following options will appear: 

•Drafting effect •Draft distance •Front downforce •Rear downforce 
•Fuel consumption rate •Incremental braking •Tire wear rate 
•AI speed percentage (50-150) •Torque spins •Centrifugal force 


Note that some of these options can be set with a negative number.