Assetto Corsa on Twitter: "IMPORTANT NOTE - Oculus Rift users: We recommend launching the game by-passing Steam VR, adding "-vr" to Steam launch options for ACC as described in the below image
Assetto Corsa Competizione Enters Steam Early Access on September 12 – GTPlanet
Racing in Assetto Corsa on the Oculus Rift DK2 is a Flawed Revelation – Road to VR