used Disc 2 strictly as an "Installation Disc". While you can play the game with just Disc 1, you’d be missing a massive chunk of the experience: A Massive Car Expansion : Installing Disc 2 adds nearly 250 additional cars to the career mode, spanning eras from 1950 to 2011. The Autovista Experience : A significant portion of the high-detail Autovista mode
In 2011, the sheer scale of Forza Motorsport 4 exceeded the ~8GB storage limit of a single Xbox 360 dual-layer DVD. To solve this, split the game into two parts:
Play through the initial tutorial races and basic settings until you reach the main menu.