Cheats:

Big Head Mode
For the bikers to have larger heads, simply type "big heads" at the main menu.

Quick Recovery
Press the [TAB] key to reset your player immediately on the bike to continue racing. This is extremely helpful if you're racing others and you fall. You don't have to wait for the cinematics of you falling or waste time getting back on the bike.

Rainbow Studios
When playing, press [ALT]+[TAB]+[A] like you meant to switch screens. When you open up MCM2 again, the ground will be Rainbow Studios' pattern. To remove this, simply restart your race.